| Cassero Senese | |
| Location: | Grosseto, Tuscany, Italy |
| Coordinates: | 42.7618°N 11.1165°W |
| Map Type: | Italy |
| Map Size: | 200 |
| Type: | Keep |
| Built: | 1345 |
| Builder: | Republic of Siena |
| Materials: | Stone |
| Condition: | Well-preserved or intact |
| Ownership: | City of Grosseto |
| Open To Public: | Daily |
The Cassero Senese (English: Sienese Keep) is a 14th-century fortification located in Grosseto, Tuscany, Italy.
Built by the Republic of Siena, it survived the demolition of the Sienese fortifications ordered by Cosimo I de' Medici, Grand Duke of Tuscany in 1565 and was incorporated in the Bastione Fortezza (Fortress Bastion) of the Grosseto city walls.