The Agatsuma River (吾妻川, Agatsuma-gawa) is a major river in the northern Kantō region of Japan. It is 76.22 kilometres (47.36 mi) in length and has a drainage area of 1,366 square kilometres (527 sq mi). Located entirely within Gunma Prefecture, it is one of the prefecture's major rivers. It is also a major tributary of the Tone River.