| Official Name: | San Sebastián |
| Settlement Type: | Municipality |
| Pushpin Map: | Guatemala |
| Pushpin Label Position: | bottom |
| Pushpin Map Caption: | Location in Guatemala |
| Subdivision Type: | Country |
| Subdivision Name: | Guatemala |
| Subdivision Name1: | Retalhuleu Department |
| Leader Title: | Mayor |
| Unit Pref: | Imperial |
| Area Total Km2: | 28.4 |
| Population As Of: | 2018 census |
| Population Footnotes: | [1] |
| Population Total: | 29167 |
| Population Density Km2: | auto |
| Population Urban: | 9362 |
| Population Blank2 Title: | Religions |
| Elevation M: | 309 |
| Blank Name: | Climate |
| Blank Info: | Am |
San Sebastián is a town and municipality in the Retalhuleu department of Guatemala.