| Castelletto d'Erro | |
| Official Name: | Comune di Castelletto d'Erro |
| Coordinates: | 44.6333°N 32°W |
| Region: | Piedmont |
| Province: | Alessandria (AL) |
| Mayor: | Giuseppe Panaro |
| Area Total Km2: | 4.7 |
| Population Total: | 155 |
| Population As Of: | 3 June 2017[1] |
| Population Demonym: | Castellettesi |
| Elevation M: | 544 |
| Saint: | St. Anne |
| Day: | 26 June |
| Postal Code: | 15010 |
| Area Code: | 0144 |
Castelletto d'Erro is a comune (municipality) in the Province of Alessandria in the Italian region Piedmont, located about 70km (40miles) southeast of Turin and about 35km (22miles) southwest of Alessandria.
Castelletto d'Erro borders the following municipalities: Bistagno, Cartosio, Melazzo, Montechiaro d'Acqui, and Ponti.