Karel Petr (Czech: ['kar?l 'p?tr?]; 14 June 1868, Zbyslav, Austria-Hungary – 14 February 1950, Prague, Czechoslovakia) was one of the most renowned Czech mathematicians of the first half of the 20th century.
Eduard Cech was a doctoral student of Petr in Charles University, Prague.
Petr's doctoral students also included Bohumil Bydžovský and Václav Hlavatý.