Jaroslav Fragner (25 December 1898 - 3 January 1967) was a Czech architect and teacher. He was born into an old Prague patrician family and he was a member of the noteworthy avant-garde association Devetsil.

In the 20's his style evolved from synthetic Cubism to the international version of Functionalism. He saw its abstract boxlike forms as the expression of new Humanism based on geometry. In public buildings he was primarily interested in the issue of modern monumentality. After the communist coup d'etat in 1948, he adopted - unwillingly - the principles of socialist Realism. He left his mark in Prague through the audacious, sensitive or also less sensitive reconstructions and completions of historic buildings, in which he specialized since the 40's. Some of his major works are the renovation of the Bethlehem Chapel and of the Karolina complex, the medieval seat of the Charles University.