| San Costanzo | |
| Official Name: | Comune di Costanzo |
| Coordinates: | 43.7667°N 17°W |
| Region: | Marche |
| Province: | Pesaro e Urbino (PU) |
| Frazioni: | Cerasa, Marotta, Solfanuccio, Stacciola |
| Mayor: | Filippo Sorcinelli |
| Area Total Km2: | 40.89 |
| Population Footnotes: | [1] |
| Population Total: | 4786 |
| Population As Of: | 31 December 2015 |
| Population Demonym: | Sancostanzesi |
| Elevation M: | 150 |
| Istat: | 041051 |
| Postal Code: | 61039 |
| Area Code: | 0721 |
San Costanzo is a comune (municipality) in the Province of Pesaro e Urbino in the Italian region Marche, located about 40km (30miles) northwest of Ancona and about 20km (10miles) southeast of Pesaro.
The municipality of San Costanzo contains three frazioni (subdivisions, mainly villages and hamlets) Cerasa, Solfanuccio, and Stacciola. A minor portion of Marotta belongs to the municipality.
San Costanzo borders the following municipalities: Fano, Mondolfo, Monte Porzio, Monterado, Terre Roveresche.