| Castellar Guidobono | |
| Official Name: | Comune di Castellar Guidobono |
| Coordinates: | 44.9°N 64°W |
| Region: | Piedmont |
| Province: | Alessandria (AL) |
| Mayor: | Stefano Arrigone |
| Area Total Km2: | 2.48 |
| Population Footnotes: | [1] |
| Population Total: | 398 |
| Population As Of: | 30 June 2017 |
| Population Demonym: | Castellaresi |
| Elevation M: | 144 |
| Postal Code: | 15050 |
| Area Code: | 0131 |
Castellar Guidobono is a comune (municipality) in the Province of Alessandria in the Italian region Piedmont, located about 100km (100miles) east of Turin and about 25km (16miles) east of Alessandria.
Castellar Guidobono borders the following municipalities: Casalnoceto, Viguzzolo, and Volpeglino.
Linked to the municipality of Tortona, whose destiny it followed, it was a fief of the Guidobono Cavalchini family of Monleale, from which it derives its name.