Keijuro Matsui (popularly known as KJ) (born October 16, 1985) is a Japanese professional basketball player for the Kagawa Five Arrows of the B.League.

He is a former guard for the Columbia Lions basketball team at Columbia University and the first Japanese native basketball player in NCAA Division I history.

Matsui also played in the 2005 Nike Hoop Summit for the World Select Team, only the second Japanese to do so.

Following his collegiate career, he relocated to his native country, where he has played ever since.

This biographical article relating to a Japanese basketball figure is a stub.