The 1988 United States Senate election in Washington was held on November 8, 1988. Incumbent Republican U.S. Senator Daniel J. Evans decided to retire instead of running for re-election to a full term, after being appointed to the seat in 1983, and won election to a partial term that same year. Republican former U.S. Senator Slade Gorton, who had just lost a re-election bid in 1986, won the open seat. As of 2024, this is the last time Washington simultaneously voted for different parties for president and for senate, as Democrat Michael Dukakis won the state in the concurrent presidential election.
Mike Lowry, the Democratic nominee, would run successfully for Governor of Washington in 1992.