In August 2001, the St. Louis Cardinals claimed Cairo on waivers from the Cubs. He remained with the Cardinals through the 2003 season. He hit .333 in 27 games in 2001, .250 in 108 games in 2002 and .245 in 92 games in 2003. He also appeared in the postseason for the first time in his career in 2001. In the 2002 National League Championship Series against the San Francisco Giants he had five hits, including a home run, in 13 at-bats.