Stein's final season with the Seattle Mariners would come in 1980. On April 29, against the Minnesota Twins, Stein had a season high four hit game. He matched that high on July 26, against the Toronto Blue Jays. On July 28, Stein broke up a no-hit bid by Cleveland Indians pitcher Len Barker. In his final season with the Mariners, Stein batted .268 with 16 runs scored, 53 hits, five doubles, one triple, five home runs, and 27 RBIs in 67 games played. Defensively, he played 34 games at third base, 14 games at second base, and eight games at first base. He also played five games that season as Seattle's designated hitter.