Castelli is an Italian surname. Notable people with the surname include:
Alfredo Castelli (born 1947), Italian comic book author
Benedetto Castelli (1577–1643), Italian mathematician
David Castelli (1836–1901), Italian scholar and educator in the field of secular Jewish studies
Ignaz Franz Castelli, (1780–1862), Austrian dramatist
Juan José Castelli (1764–1812), Member of the first national government of Argentina
Leo Castelli (1907–1999), American art dealer
Michelangelo Castelli (1808–1875), Italian politician
Roberto Castelli (born 1946), Former Italian Minister of Justice
