| Pietrosul | |
| Name Other: | Köves-Somlyó |
| Pushpin Map: | Romania |
| Subdivision Type1: | Country |
| Subdivision Name1: | Romania |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Harghita County |
| Length: | 13km (08miles) |
| Source1: | Harghita Mountains |
| Mouth: | Mureș |
| Mouth Coordinates: | 46.7315°N 25.4385°W |
| Basin Size: | 40km2 |
The Pietrosul (Hungarian: Köves-Somlyó or Köves-Somlyó-patak; Hungarian pronunciation: NaNk) is a left tributary of the Mureș in Romania. It flows into the Mureș between Joseni and Remetea. Its length is 13km (08miles) and its basin size is 40km2.