Daudnagar (ISO: Dāūdanagara) is a town and the subdivisional headquarter of Daudnagar Subdivision in Aurangabad district in the state of Bihar, India under the Magadh division. Until 1991, there was only one Subdivision in the Aurangabad district: Aurangabad Sadar. On 31 March 1991, one other subdivision, Daudnagar, was created. Daudnagar is a 200-year-old historical city and its living proof is Daudnagar has an old historical fort situated on the eastern bank of the Son River. National Highway NH139 which connects Jharkhand's Palamu district to Patna, passes through the town.

Daudnagar was founded by Daud Khan. The area between Daudnagar and Aurangabad assumed great strategic importance when Daud Khan, Aurangzeb's Subedar in Bihar, marched against the Raja of Palamu. As a mark of victory against the Raja in the year 1664, Daud Khan founded the city of Daudnagar. Daud Khan Qureshi was an Indian Muslim Shaikhzada native of Hisar (city) in Haryana, then called Hisar Firuza. The surrounding area was also granted to him as a Jagir by the emperor. Early in the 18th century, Buchanan saw it as a flourishing town with cloth and opium factories. The Sarai, built by Daud Khan was possibly intended to serve as a stronghold, as it was well-fortified with a battlemented wall, two large gates and a surrounding moat. In the outlying part of the town, called Ahmadganj, lies the tomb of Ahmad Khan.

Daudnagar is located at 25°02′N 84°24′E / 25.03°N 84.4°E / 25.03; 84.4. It has an average elevation of 84 metres (275 feet).

Daudnagar is situated on the bank of the Son River, and NH139 passes through the town. It is situated 30 kilometres (19 mi) away from the district headquarter Aurangabad The Indrapuri Barrage canal also passes through the town.

As of 2011^[update] India census, Daudnagar town has population of 52,364, male population is 27,493 and female population is 24,871. There are 9003 children age 0-6, which is 17.19% of population. The town's female sex ratio is 905 against state average of 918. The child sex ratio in Daudnagar is around 957 compared to the Bihar state average of 935. The literacy rate of the town is 67.51%, which is higher than the state average of 61.80%. Male literacy is around 74.72%, while female literacy rate is 59.44%. Hindus are majority in the town with 80.80% of the population while Muslims constitute 18.78%. Followers of the other religions including Christian, Jain, Sikh, Buddhist also live in Daudnagar but their population is minuscule, just 0.42% of the total population. Schedule Caste (SC) constitutes 12.83% while Schedule Tribe (ST) are 0.08% of the population.

Daudnagar was first identified as a town and given the status of Nagar Panchayat in 1885. The town's population increased from 37,000 in 2001 to more than 52,000 in 2011, which made it eligible for the status of municipal council. Hence, in 2017, the urban development and housing department of the Bihar government, by a notification, upgraded the local governing body from Nagar Panchayat to Nagar Parishad. The Nagar Parishad Daudnagar has been mandated to oversee the day to day administration of the town and provides various services to the residents including sanitation, sewage and drain, door to door municipal solid waste collection and disposal, potable water supply, street lights, roads etc.

The municipal authorities are as follows:

The Daudnagar Subdivision is headed by a SDM who is usually the officer of Indian Administrative Service(IAS) or Bihar Administrative Service. Daudnagar subdivision comprises four blocks, each headed by a Block Development Officer (BDO).