1990–91 Washington State Cougars men's basketball team

The 1990–91 Washington State Cougars men's basketball team represented Washington State University for the 1990–91 NCAA Division I men's basketball season. Led by fourth-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 16–12 overall in the regular season and 8–10 in conference play, tied for fifth in the standings.

There was no conference tournament this season; last played in 1990, it resumed in 2002.