1989–90 Washington State Cougars men's basketball team

The 1989–90 Washington State Cougars men's basketball team represented Washington State University for the 1989–90 NCAA Division I men's basketball season. Led by third-year head coach Kelvin Sampson, the Cougars were members of the Pacific-10 Conference and played their home games on campus at Beasley Coliseum in Pullman, Washington.

The Cougars were 7–21 overall in the regular season and 1–17 in conference play, last in the standings. The sole Pac-10 victory was by one point over USC on November 30, and the season's last win was on December 29.

At the conference tournament, the Cougars met seventh seed USC in the first round and lost by seventeen points, ending the season on an eighteen-game losing streak.

Postseason result
!colspan=5 style=| Pacific-10 Tournament