Koshi Province (Nepali: कोशी प्रदेश),is one of the seven federal provinces of Nepal. It was established in 2015 by the current constitution of Nepal. It was originally called Province No. 1. On March 1, 2023, it was renamed after the Kosi River. The capital city is Biratnagar.
The province is bordered by the Tibet of China to the north, the Indian states of Sikkim and West Bengal to the east, and Bihar to the south, and Bagmati Province and Madhesh Province to the west. According to the 2021 Nepal census, there are around 5 million people in the province, with a population density of 190 per square kilometre. As per the 2011 Nepal census the province had around 4.5 million people.