The Bihar Subah (Persian: صوبه بهار) was a province (suba) of the Mughal Empire that was formed in 1575 CE.

The seat of Azimabad was named after the Mughal prince, Azim-ush-Shan who was the son of Emperor Shah Alam I.

On its northern boundary, it reached into the foothills of the Himalayas although this border was poorly defined as it was covered by the forested Terai.

Under Emperor Akbar, Bihar was divided into seven sarkars which were:[1] Much of the region was now fully integrated into the Empire, particularly around Monghhy and Khokhrah where it was said that "the laws and commands of the provincial administration could be ignored without incurring too many problems."

The sarkar of Purnea was not fully integrated into the suba of Bihar but was under an independent faujdar known as the Faujdars of Purnea which acted as a small military frontier between Bihar and Bengal.