1988 Seattle Mariners season

The Seattle Mariners 1988 season was their 12th since the franchise creation, and ended the season finishing seventh in the American League West with a record of .420.

Offseason

 * December 9, 1987: Phil Bradley and Tim Fortugno were traded by the Mariners to the Philadelphia Phillies for Glenn Wilson, Mike Jackson, and Dave Brundage (minors).
 * December 21, 1987: John Moses was released by the Mariners.
 * December 22, 1987: Lee Guetterman, Clay Parker, and Wade Taylor were traded by the Mariners to the New York Yankees for Steve Trout and Henry Cotto.
 * January 19, 1988: John Rabb was signed as a free agent by the Mariners.

Regular season

 * Mark Langston became the ace of the pitching staff as he led the club in wins (15) and strikeouts (235).

Opening Day starters

 * Mickey Brantley
 * Alvin Davis
 * Mike Kingery
 * Ken Phelps
 * Jim Presley
 * Rey Quiñones
 * Harold Reynolds
 * Steve Trout
 * Dave Valle
 * Glenn Wilson

Notable transactions

 * May 23, 1988: John Christensen was released by the Mariners.
 * June 1, 1988: Steve Balboni was signed as a free agent by the Mariners.
 * June 1, 1988: Greg Pirkl was drafted by the Mariners in the 2nd round of the 1988 Major League Baseball Draft. Player signed June 6, 1988.
 * June 8, 1988: Manager Dick Williams was fired and replaced by interim manager Jim Snyder.
 * July 21, 1988: Ken Phelps was traded by the Mariners to the New York Yankees for Jay Buhner, Rich Balabon (minors) and a player to be named later. The Yankees completed the deal by sending Troy Evers (minors) to the Mariners on October 12.
 * July 22, 1988: Glenn Wilson was traded by the Mariners to the Pittsburgh Pirates for Darnell Coles.

Major League debuts

 * Batters:
 * Greg Briley (June 27)
 * Bill McGuire (Aug 2)
 * Pitchers:
 * Erik Hanson (Sep 5)
 * Mike Schooler (June 10)
 * Terry Taylor (Aug 19)

Starters by position
''Note: Pos = Position; G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Other batters
''Note: G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

Starting pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Other pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Relief pitchers
Note: G = Games pitched; W = Wins; L = Losses; SV = Saves; ERA = Earned run average; SO = Strikeouts

Farm system
AZL club affiliation shared with Boston Red Sox