Castelnuovo is an Italian surname which loosely translates as Newcastle in English. Notable people with the surname include:
Emma Castelnuovo (1913–2014), Italian mathematician and teacher Enrico Castelnuovo (1839–1915), Italian writer Guido Castelnuovo (1865–1952), Italian mathematician Mario Castelnuovo-Tedesco (1895–1968), Italian composer Nino Castelnuovo (1936–2021), Italian actor