Siwan is a city and nagar parishad in the Indian state of Bihar.

The weather of Siwan is generally mild cool throughout the year and temperature falls down up to 4 °C in December and January but it is warm in May, June and July.

As of 2011 Indian Census, Siwan had a total population of 135,066, of which 70,756 were males and 64,310 were females.

[3] As of 2001[update] India census, Siwan had a population of 108,172 of which 57,223 were male and 50,949 female.

Small populations of followers of Christianity, Sikhism, Buddhism and Jainism are also present in the city.

Bihar State Highway-47 connects Barharia, Mairwa and Guthani to Siwan.