| Siamaggiore | |
| Official Name: | Comune di Siamaggiore |
| Native Name: | Siamaiore/Siamajori |
| Pushpin Map: | Italy Sardinia |
| Coordinates: | 39.95°N 46°W |
| Region: | Sardinia |
| Province: | Oristano (OR) |
| Frazioni: | Pardu Nou |
| Mayor: | Giuseppino Piras |
| Area Total Km2: | 13.2 |
| Population Total: | 1005 |
| Population As Of: | Dec. 2004[1] |
| Population Demonym: | Siamaggioreresi |
| Saint: | St. Constantine Emperor |
| Day: | 23 aprile |
| Postal Code: | 09070 |
| Area Code: | 0783 |
Siamaggiore (Sardinian: Siamaiore[2] [3] or Siamajori) is a comune (municipality) in the Province of Oristano in the Italian region Sardinia, located about 90km (60miles) northwest of Cagliari and about 7km (04miles) northeast of Oristano.
Siamaggiore borders the following municipalities: Oristano, Solarussa, Tramatza, Zeddiani.