Petrus Johannes "Piet" Keizer (14 June 1943 – 10 February 2017) was a Dutch footballer. He played as a left winger. He played for Ajax his whole career from 1961 to 1974. He made 365 league appearances for Ajax. He also played 34 games for the Netherlands national football team, scoring eleven goals. He retired in 1974 after an argument with Hans Kraay Sr., then-manager of Ajax.