Rajauli is a tehsil, block and subdivision (sub–district) in Nawada district of Magadh division of the Indian state of Bihar. The tehsil of Rajauli is located at a distance of about 30 kilometres (19 mi) from Nawada city on National Highway 20 (previously numbered as NH31) and is situated on the bank of Dhanarjay river. Rajauli, a Scheduled Caste (SC) reserved Assembly Constituency (AC) seat, had a total of 302900 electors during the 2015 Bihar Legislative Assembly election. Rajauli subdivision consists of 95 panchayats and 688 revenue villages while Rajauli block consists of 17 panchayats and 169 revenue villages.

The hills in Rajauli's neighbourhood have religious significance for Hindus and many legends are attached to them. Rishis such as Shringi, Durvasa, Gautama and Lomasa have their ashrams on eponymously named peaks here. Veer Lorik, the Ahir cowherd hero, is said to have been born in the area and was the reason for the bountiful cultivation in and around Rajauli at one time. Rajauli has a Sikh connection including a visit by Guru Nanak. The Gurudwara Rajauli Sangat, one of the largest sangats in the state, is in Rajauli and is part of Bihar Tourism's "Guru Circuit".

Francis Buchanan-Hamilton passed through Rajauli during his surveys of Patna and Gaya in 1811–1812. He kept a journal in which he wrote on 14 December 1811, "[…] the town of Rajauli situated among fine mango groves. These were all planted by a Fakir, a most venerable personage, by whom I was visited on my arrival. He is a Saiud born at Baragong near Mirzapur, and after some adventures in the west came and sat down here in the midst of wild beasts and the devils worshipped by the Infidels. After a residence of 25 years he attracted the notice of Kamgar Khan, from who he obtained a considerable grant of lands, which he has brought into cultivation and ornamented with fine plantations."

An Archaeological Survey of India report by J D Beglar in 1872–73 mentions that the hills of Rajauli "are in their way deserving of mention", as they are said to have been home to the Saptarishis (transl. seven Rishis or sages). The peaks here are named after a number of saints. Singar Peak, named after Sringi Rishi, is ascended by devotees while at the base an annual fair takes place. The 1873 survey report also mentioned an annual fair at Ektara, Mahabar hill, Satgaon — "Ektâra is a small place of pilgrimage situated in the wild Rajauli Hills at the source of the Dhanarjeh river which flows past Rajauli; here is a very picturesque waterfall and a small rock cell; not far from here I see "rock temples" marked in the Indian Atlas sheet, but my enquiries for them were vain." Other rishis including Durvasa, Lomasa and Gautama lived in Rajaulis neighbourhood; with their ashrams also housing Goddess Durga and Goddess Indra, the later to whom villagers use to pray during times of drought. Dubaur, 15 kilometers south of Rajauli, claims to be the birthplace of Goala (Ahir) Veer Lorik. Lorik is said to have been the force behind Rajauli's transformation into a cultivated plain. Buchanan wrote that Dubaur is "a village of Bhunghiyas belonging to Brijomohun Saha, a Ghatwal".

By 1875, Bihar to Rajauli was a metaled road, a rarity in the region at the time. The Maksudpar estate, which in 1900–04 included 160 villages, covered 130 square miles (340 km) of which about 60 square miles (160 km) of land was in and around Rajauli. In 1901, the population of Rajauli village was 1509. It was connected to Nawada, 18 km to the north, by a metaled road. Rajauli was an important market for the neighbouring hills.

In 1906 L.S.S. O'Malley of the Indian Civil Service wrote that Rajauli, "possesses and excellent system of drainage, which dates back to the time it was a municipality. The drains are of cement, but since the abolition of the municipality they have been neglected and have become silted up. Rajauli contains a police-station, a branch establishment of the Nanakpanthi monastery at Akbarpur (8 miles to the north), and a Muhammadan charitable endowment, in which there is a sacred fire said to have been lit 300 years ago by fire brought from Mecca."

Rajauli's neighbourhood also had granite and mica mines which were described by explorers and surveyors. In 1838, Robert Montgomery Martin described these in detail after a visit, also mentioning the presence of "felspar" (however most of these locations are now in Jharkhand).

A large fort-like building in the center of the town is called 'sangat', meaning "a body of men and women who meet religiously specially in presence of the 'Guru Granth Sahib'". It is one of the largest sangats in Bihar. The Directorate of Tourism of the Government of Bihar places Gurdwara Rajauli Sangat in its official "Guru Circuit":

Gurdwara Rajauli Sangat, which is about 4 acres in Rajauli has the khapar of Bhagat Bhagwan, presented to him by Hingraj Devi Sangat. This 200 year old holy place of worship comprises of about 50 residential rooms. One can take a glimpse of the 100 year old handwritten bir of Guru Granth Sahib and some Hindu deities. There are some Samadhis and gates in the complex with the name of Baba Sandbux Das written in Gurmukhi.

— Guru Circuit pamphlet, Bihar Tourism

Francis Buchanan-Hamilton wrote in 1811 that Rajauli "has a Sanget of the followers of Nanak, a large neat–looking place with a tiled roof".

Guru Nanak is said to have stopped at Rajauli. In Dr Trilochan Singh's biography of Guru Nanak he writes, "Rajauli bears witness to the fact that the Buddhist sages of this area accepted the teachings of Guru Nanak and established permanent centres of Guru Nanak’s school of thought in this region".

A fair during Guru Nanak Gurpurab takes place here. There is a Khankah at some distance from the Sangat.

Rajauli is situated along the Dhanarjay river on NH 20 (previously numbered as NH31). It is 30 kilometres (19 mi) from the district city Nawada and 144 kilometres (89 mi) from Patna. Rajauli is a sub-division that borders the state of Jharkhand, and has an elevation of 135 m above sea level. Rajauli is mainly surrounded by small and mid-range mountains including Lomash Rishi and Shringi Rishi mountains. More than 100 villages make up Rajauli subdistrict. Rajauli was once home to monsoon and prairie forest. The principal trees were sakhua, paisar, khair, Shisham, parmi, salaiya simar, kendu and peepal. The forest and wild life have almost completely disappeared. Gautam Budha Wildlife Sanctuary is nearby.