Arnaldi is an Italian surname. Notable people with the surname include:
Girolamo Arnaldi (1929–2016), Italian historian Matteo Arnaldi (born 2001), Italian tennis player Rinaldo Arnaldi (1914–1944), Italian Resistance member
See also Arnaldo, given name Castrum Arnaldi, castle in Israel Megacraspedus arnaldi, species of moth Villa Arnaldi, historical edifice in Vicenza, Italy