Castelnovo di Sotto (Reggiano: ) is a comune (municipality) in the Province of Reggio Emilia in the Italian region Emilia-Romagna, located about northwest of Bologna and about northwest of Reggio Emilia.
Castelnovo di Sotto borders the following municipalities: Boretto, Cadelbosco di Sopra, Campegine, Gattatico, Gualtieri, Poviglio.
It is home of one of the most ancient carnivals in Italy, dating from the 16th century.