| Castelo de Montemor-o-Velho | |
| Location: | Montemor-o-Velho, Portugal |
| Type: | Medieval fortress |
| Built: | 1088–1520 |
| Builder: | Alfonso VI of León and Castile |
| Condition: | Intact |
| Ownership: | Portuguese Republic |
The Castle of Montemor-o-Velho (Portuguese: Castelo de Montemor-o-Velho) is a Portuguese castle in the civil parish of Montemor-o-Velho e Gatões, municipality of Montemor-o-Velho, district of Coimbra.
It has been listed as a national monument since 1910. It is older than Portugal's nationality (1139).
Since 2014, the castle hosts the Festival Forte which is an electronic music festival set in August.