| Clubname: | Castelsardo |
| Fullname: | Unione Sportiva Dilettantistica Castelsardo |
| Nickname: | – |
| Founded: | 1958 |
| Ground: | Stadio Comunale, Castelsardo, Italy |
| Capacity: | 1,000 |
| Chairman: | Antonio Giuseppe Bayslak |
| Manager: | Rosario Affuso |
| League: | Serie D/G |
| Season: | 2008–09 |
| Position: | Serie D/G, 14th |
| Pattern B1: | _thinbluesides |
| Leftarm1: | FF0000 |
| Body1: | FF0000 |
| Rightarm1: | FF0000 |
| Shorts1: | 0000FF |
| Socks1: | FF0000 |
| Pattern B2: | _redbluerightsash |
| Leftarm2: | FFFFFF |
| Body2: | FFFFFF |
| Rightarm2: | FFFFFF |
| Shorts2: | FFFFFF |
| Socks2: | FFFFFF |
Unione Sportiva Dilettantistica Castelsardo is an Italian association football club located in Castelsardo, Sardinia. It currently plays in Serie D. Its colors are red and blue.