Đồng Nai is a province in the Southeast region of Vietnam, located east and northeast of Ho Chi Minh City (Saigon). The capital city and the largest city in Đồng Nai is Biên Hòa.

Đồng Nai is in southeastern Vietnam and bordered by: Bình Thuận, Lâm Đồng, Bình Dương and Bình Phước, Bà Rịa–Vũng Tàu, and Ho Chi Minh City (Saigon). Đồng Nai has an advanced traffic system with many backbone national roads crossing it, such as: National Route 1A, National Route 20, National Route 51 and the North–South railway lines; located adjacent to the Saigon Port and Tan Son Nhat International Airport, it offers many advantages to economic activities in the area. Its location is very important for the development of the Southern economic main hub and a junction of the South Eastern and Tây Nguyên Highland.

Đồng Nai is based essentially on the system of lakes, dams and rivers, of which Trị An Lake with an area of 323 km² and over 60 rivers, rivulets and canals are very favorable for the development of a number of aquatic products: raft bred fish and shrimp. The seasonal tropical forests are protected in Cát Tiên National Park, located in the north of Đồng Nai and the adjacent Vĩnh Cửu Nature Reserve; the former has been recognized internationally as a significant biosphere reserve. From the mountainous area, Đồng Nai River, Vietnam's largest internal waterway, flows southeast through Biên Hòa City, Ho Chi Minh City, and villages along its way. This river plays a crucial role in providing fresh water for the entire region.

Đồng Nai lies in the monsoon tropical zone and is affected by the north-east and south-west monsoon. It is also under the influence of the Pacific Ocean tropical atmosphere between April and October. The climate is divided into two distinct seasons: the rainy season lasts from March or April to November and the dry season from December to March or April of the following year. The average temperature is between 23.9 and 29.0 °C, much lower than the standard level of tropical regions (26-30 °C). Its annual rainfall is quite high with 1,500 - 2,700 mm.

On average, the weather is sunny for 4.0-9.5 hours a day and does not exceed 11.5 hours per day, even on the hottest and sunniest days. Total rainy days within a year are between 120 and 170 days (the standard level of tropical regions is 150–160 days) with a total rainfall of some 1,500 - 2,750 mm. The average humidity is around 80 - 82% and humidity in the dry season is 10-12%, lower than that of the rainy season; humidity varies considerably between areas.

Đồng Nai's weather with regular sunshine, rain, and high humidity, equally found in the localities, facilitates agricultural production and development of industrial, cultural and tourist activities.

Đồng Nai is plentiful with resources such as forests, granite mines, construction stone, clay, kaolin, pozzolan, sand and gravel.

Đồng Nai is one of Vietnam's most populous provinces (ranked fifth) with a population of 2,838,600 in 2014. Its population has been growing rapidly in recent years, mainly driven by migrant workers coming to the province to work in factories. Population growth was 1.95% in 2005, between 2.5% from 2008 to 2010 and 3.5% in 2011. Net migration contributed 2.2% to this figure. Đồng Nai is second only to Bình Dương province in both population growth and net migration.

The population of Đồng Nai is primarily the dominant Kinh (Viet) ethnicity, although there are residents of the Chinese, Stieng, Mạ, Nùng, Tay, and Cham minorities.

Đồng Nai has made significant progress in upgrading its transport infrastructure, especially roads. National highways in the province have a total length of 244.5 km and have been improved and widened up to level 1 and 2 standards (National Highway No. 5 and 6) or up to third grade like National Highway No. 20 to Đà Lạt. The total roads system in the province is 3,339 kilometers long, of which almost 700 kilometers are tar roads. All communes and wards are connected to the road network.

Under scheme in the near future, highways to Bà Rịa–Vũng Tàu province and Ho Chi Minh City, a railway connecting Biên Hòa to Vũng Tàu, upgrading provincial road No. 726 and connecting National Highway No. 20 and No. 1 with National Highway No. 51 will create a complete system, promoting socioeconomic development in the province and region.

A new airport, Long Thành International Airport, is planned for construction in Long Thành district, Đồng Nai, approximately 40 km northeast of Ho Chi Minh City. Upon completion, it will handle international flights in place of Tan Son Nhat International Airport, which will serve domestic flights.

Đồng Nai is subdivided into 11 district-level sub-divisions:

• 9 districts:
  • Cẩm Mỹ
  • Định Quán
  • Long Thành
  • Nhơn Trạch
  • Tân Phú
  • Thống Nhất
  • Trảng Bom
  • Vĩnh Cửu
  • Xuân Lộc
• 2 provincial cities:
  • Biên Hòa (capital)
  • Long Khánh

They are further subdivided into eight commune-level towns (or townlets), 122 communes, and 40 wards.

District-level sub-divisions	Biên Hòa city	Long Khánh city	Cẩm Mỹ district	Định Quán district	Long Thành district	Nhơn Trạch district	Tân Phú district	Thống Nhất district	Trảng Bom district	Vĩnh Cửu district	Xuân Lộc district
Area (km²)	264.08	191.75	468	970.5	431.01	411	802.4	250.2	328.17	1,095.7	725.84
Population	1,272,000	245,040	182,010	225,160	534,150	401,720	190,670	195,280	558,050	187,430	253,140
Density (people/km²)	4,817	1,278	391	232	1,239	977	238	780	1,700	171	348
Administrative divisions	29 wards, 1 commune	11 wards, 4 communes	13 communes	1 townlet, 13 communes	1 townlet, 13 communes	1 townlet, 11 communes	1 townlet, 17 communes	1 townlet, 9 communes	1 townlet, 16 communes	1 townlet, 11 communes	1 townlet, 14 communes
Year of establishment	1976	2019	2003	1991	1994	1994	1991	2003	2003	1994	1991

Đồng Nai is one of Vietnam's main manufacturing centers and one of the most developed provinces.

Despite its strong focus on industrial development, Đồng Nai still has a substantial agricultural sector. Agricultural land accounts for 47% of the province's area as of 2011, a total of 277,600 ha. This is lower than in other provinces in the Southeast region, except for Ho Chi Minh City. Cereals were grown on 118,600 ha in 2011, an area that has been decreasing gradually in recent years, from 139,300 ha in 2005. The output of rice has, however, remained stable and was at 335,200t in 2011. The province also produced 305,300t of maize, making it the largest producer of maize outside the country's mountainous regions and contributing 6.3% to the national maize output. Đồng Nai also produced 619,700t of sugar cane (3.5% of the national output), sweet potatoes and cassava.

Đồng Nai is the largest livestock producer among Vietnam's provinces and there are plans to further invest in the sector. The government reserved 15,000 ha for livestock farming in 2012, mostly for poultry and pigs. In 2011 there were 1.33 million pigs and 10.655 million poultry. Despite not being located along the coast, Đồng Nai produced 41,600t of fishery products in 2011. Over 90% of this was produced in 33,500 ha of aquaculture farms. This makes Đồng Nai the largest aquaculture producer outside the Mekong Delta.

Đồng Nai is one of Vietnam's main manufacturing centers. It has attracted 9.1% of FDI into Vietnam by 2011, an accumulated US$18.2 billion, the fourth largest after Ho Chi Minh City, Bà Rịa–Vũng Tàu province and Hanoi. Industrial gross output in 2011 was VND 314 trillion, 10.6% of the national value. It has received a broad range of FDI projects, including a Bosch auto component plant, a Toshiba motor plant, a PepsiCo beverage factory, a Posco steel plant, and a Nestlé coffee factory.

On Vietnam's Provincial Competitiveness Index 2023, a key tool for evaluating the business environment in Vietnam’s provinces, Dong Nai received a score of 66.28. This was an improvement from 2022 in which the province received a score of 65.67. In 2023, the province received its highest scores on the 'Time Costs' and 'Business Support Policy' criterion and lowest on 'Policy Bias' and 'Labour Policy'.

A large part of Đồng Nai Biosphere Reserve, include Nam Cát Tiên, is located in Dong Nai province.

Tri An Dam, besides providing electricity, it also helps to regulate floods and ensure drinking water for people in the area.

As a result of the Vietnam War, some areas around Bien Hoa Air Base were dioxin pollution. The authorities are trying to clean up these areas.

As defined by a 2008 World Bank survey, the province is one of the five most-polluted in Vietnam.

• Đồng Nai University
• Lạc Hồng University
• Lương Thế Vinh high school
• Ngô Quyền high school
• Vietnam Police Fire Prevention & Fighting University (T06/K56) campus Southern
• Vietnam People's Security University (T04/T47) campus in Đồng Nai province
• Second Army Officer University school – Nguyễn Huệ University
• Vietnam People's Security College (T08)
• Branch of Vietnam National University of Forestry in Đồng Nai province
• Eastern University of Technology
• Đồng Nai University of Technology
• Lê Quý Đôn College
• Technology and Management Sonadezi College
• Đồng Nai High Technology College
• Đồng Nai Technical College
• Đồng Nai Medical College

• Đồng Nai Provincial People's Council & People's Committee
• Đồng Nai Provincial People's Council & People's Committee (in Vietnamese)
• Đồng Nai Industrial Service, a provincial department of the Ministry of Industry