| Official Name: | Koseč |
| Pushpin Map: | Slovenia |
| Pushpin Label Position: | bottom |
| Pushpin Map Caption: | Location in Slovenia |
| Subdivision Type: | Country |
| Subdivision Name: | Slovenia |
| Subdivision Type1: | Traditional region |
| Subdivision Name1: | Slovenian Littoral |
| Subdivision Type2: | Statistical region |
| Subdivision Name2: | Gorizia |
| Subdivision Type3: | Municipality |
| Subdivision Name3: | Kobarid |
| Area Total Km2: | 5.65 |
| Population As Of: | 2002 |
| Population Total: | 68 |
| Population Blank1 Title: | Ethnicities |
| Population Blank2 Title: | Religions |
| Coordinates: | 46.252°N 13.624°W |
| Elevation M: | 629.1 |
| Footnotes: | [1] |
Koseč (in Slovenian pronounced as /kɔˈsɛtʃ/; Italian: Cossis) is a small settlement above Drežnica in the Municipality of Kobarid in the Littoral region of Slovenia.
A small church in the settlement dedicated to Saint Justus dates to the second half of the 14th century, making it one of the oldest surviving churches in the Soča area. It is built of travertine and its interior is covered in frescos from the late 15th century.[2]