Thesleff is a surname. Notable people with the surname include:
Alexander Amatus Thesleff (1907–1983), Finnish diplomat and lawyer Ellen Thesleff (1869-1954), Finnish painter Irma Thesleff, Finnish biologist Jan Thesleff (born 1959), Swedish diplomat Rolf Thesleff (1878–1938), Finnish educator and diplomat Wilhelm Alexander Thesleff (1880-1941), Finnish general