Petrus Johannes "Piet" Keizer (14 June 1943 – 10 February 2017) was a Dutch professional footballer who played as a left winger.

As part of the "Total Football" Ajax Amsterdam team of the 1960s and 1970s, Keizer was particularly notable during the successive managerial tenures of Rinus Michels and Stefan Kovacs (1965–1973).

Keizer was selected by Netherlands manager, Rinus Michels, to play for the Dutch squad during the 1974 FIFA World Cup, but only started in the 0–0 draw against Sweden.

[6] Keizer suddenly retired from football in October 1974, shortly after a row over tactics with Ajax manager Hans Kraay.

[10] UEFA website has described Keizer as "the genius on the left wing, the skillfull flanker, the superb foil to Johan Cruyff".