Anna Salai (Tamil: [aɳɳaː saːlaɪ]), formerly known as St. Thomas Mount Road or simply Mount Road, is an arterial road in Chennai, India. It starts at the Cooum Creek, south of Fort St George, leading in a south-westerly direction towards St. Thomas Mount, and ends at the Kathipara Junction in Guindy. Beyond the Kathipara Junction, a branch road arises traversing westwards to Poonamallee to form the Mount-Poonamallee Road while the main branch continuing southwards to Chennai Airport, Tambaram and beyond to form Grand Southern Trunk Road (GST Road or NH45). Anna Salai, which is more than 400 years old, is acknowledged as the most important road in Chennai city. The head offices of many commercial enterprises and public buildings are located along Anna Salai. It is the second longest road in Chennai, after EVR Periyar Salai.

Several flyover projects were under consideration on the road, many of which have been shelved owing to the construction of the Chennai Metro project, which runs along the median of the road. Anna Salai Head Post office, one of the most important post offices in the city, is located on this road. It was established in 1854 as Mount Road SO as a non-gazetted delivery office. With the growth of commerce and urbanization, this SO was upgraded to gazetted in 1955. Nomenclature of this Head Post office was changed from Mount Road Head Post office to Anna Road Head Post office on 15 September 1974.

Anna Salai can be traced from at least the early 17th century, and has its origins in a cart track which was used by the European employees of the British East India Company to travel from the factory at Fort St George to the holy town of St Thomas Mount where the apostle St Thomas is believed to have been martyred, according to Christian belief. The road, in its present form, took shape during the time of Charles Macartney who served as Governor of Madras. With the construction of Marmalong Bridge in 1724, the road started gaining prominence. In the following years, the road became part of the city's central business district which originally covered only George Town. Today, most of Chennai's business and corporate offices are located on Anna Salai.

In the 1700s, the road was lined with garden houses and large colonial mansions with balconies and verandas set amidst lush gardens. By the 1800s, Mount Road has become the traders' area of the city of Madras while First Line Beach in Georgetown remained the seat of processing, shipping and manufacturing businesses. However, the business activities of Mount Road was responsible for the city's economic growth. Several giant firms had beginnings on Mount Road, from the Amalgamations group to the TVS group. The road's proximity to the Government House, the home of the Governor, and the palaces of the Nawabs of Arcot resulted in several firms selling cars and other luxury goods setting up shops on the road. Simpson & Co, which moved to its current location opposite Government Estate after 1875, began building carriages and coaches and then cars. In the early 1900s, the road became the entertainment hub for the British. In 1903, the first steam-driven car was taken for its debut drive on Mount Road. To overcome the Great Depression of the 1930s, Simpon's introduced the hire purchase system for cars and trucks. In the 1930s, the TVS group, which was a travel operator in mofussil areas, was established in Madras by acquiring the Madras Auto Service property. In the 1940s, Anantharamakrishnan helped with the formation of Amalgamations & Co. The city's first skyscraper, the LIC Building, was built on Anna Salai in 1959. Several major firms were then established, namely, Spencers & Co, Victoria Family Hotel (the present location of the Indian Overseas Bank Headquarters) and Higginbothams.

Anna Salai starts from the Parktown area of Chennai city where Chennai Central railway terminus is situated. It, then, traverses the Island with its statue of Sir Thomas Munro to the other side of the Coovum before entering the neighbourhoods of Thousand Lights and Teynampet areas. From Teynampet, it continues straight southwards to Nandanam and Saidapet before traversing the Maraimalai Adigal Bridge across the Adyar River to Little Mount and finally, Guindy. Anna Salai is maintained by the Tamil Nadu Highways Department. The road extends for a total of 11 kilometres and traverses the heart of the city.

By the 2010s, the stretch between Parry's Corner and Nandanam was used by over 16,000 vehicles during rush hour. Anna Salai is used by over 0.183 million vehicles every day. The Metropolitan Transport Corporation in Anna Salai carries about 14,000 passengers per hour per direction.

Anna Salai remains the road in the city experiencing second most number of accidents annually, next only to Jawaharlal Nehru Road (100 ft Inner Ring Road), with one person being injured every 1.13 days. Together, these roads account for almost 14 per cent of the 5,101 accidents that occurred in Chennai in 2010.

• Chintadripet MRTS railway station
• Guindy railway station

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  Anna Salai shops
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  Gemini Flyover-Anna Salai
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  Anna Salai near old Anand Theater
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  Statue of Thomas Munro in The Island, Chennai
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  The Tamil Nadu Omandurar Government Multi Speciality Hospital and Medical College
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  The offices of The Hindu and the now-defunct The Mail in Anna Salai
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  LIC Building
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  Spencer Plaza from Anna Salai
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  Thousand Lights Mosque
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  Equestrian Statue on the Nungambakkam side of Anna (Gemini) fly over.
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  Near Willingdon Bridge, seen from Chennai MRTS
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  Panagal Maaligai or Panagal Building, Saidapet

• Transport in Chennai