Nagato (Japanese 長門国; -no kuni), often called Choshu (長州 Chōshū), was a province of Japan. It was at the extreme western end of Honshu, in the area that is today Yamaguchi prefecture. Nagato bordered on Iwami and Suo Provinces.

Although the ancient capital of the province was Shimonoseki, Hagi was usually the seat of the han (fief). Nagato was ruled by the Mori clan before and after the Battle of Sekigahara.

In 1871 with the abolition of feudal domains and the establishment of prefectures (Haihan Chiken) after the Meiji Restoration, the provinces of Nagato and Suo were combined to eventually establish Yamaguchi prefecture.

Historically, the oligarchy that came into power after the Meiji Restoration of 1868 had a strong representation from the Choshu province, as Ito Hirobumi, Yamagata Aritomo, and Kido Koin were from there. Other natives famous for their role in the restoration include Yoshida Shoin, Takasugi Shinsaku,Katsura Kogoro and Kusaka Genzui among others.