The 1991 Czechoslovak Open, also known as the Prague Open was a men's tennis tournament played on outdoor clay courts at the I. Czech Lawn Tennis Club in Prague, Czechoslovakia that was part of the ATP World Series (Designated Week) of the 1991 ATP Tour.

It was the fifth edition of the tournament and was held from 5 August until 11 August 1991.

Second-seeded Karel Nováček won the singles title.

[3] Karel Nováček defeated Magnus Gustafsson 7–6(7–5), 6–2 Vojtěch Flégl / Cyril Suk defeated Libor Pimek / Daniel Vacek 6–4, 6–2