Peter Mackanin, Jr. (pronounced "ma KAN in") (born August 1, 1951) is an American former professional baseball player, scout and manager. He played in Major League Baseball as a second baseman. Mackanin most recently served as the acting manager of the Cincinnati Reds, having replaced Jerry Narron in 2007 before being replaced at season's end by Dusty Baker. He is currently the bench coach for the Philadelphia Phillies.

Mackanin was drafted by the Washington Senators in the 1969 Major League Baseball Draft and made his debut with them in 1973, after they moved and became the Texas Rangers. In a nine-year major league career, he also played for the Montreal Expos, Philadelphia Phillies, and Minnesota Twins. Mackanin's best season offensively was in 1975 when he posted a .225 batting average along with 12 home runs and 44 runs batted in.

In a nine-year major league career, Mackanin played in 548 games, accumulating 355 hits in 1,570 at bats for a .226 career batting average along with 30 home runs, 141 runs batted in and an on base percentage of .263. He ended his career with a .968 fielding percentage.