| Martonca | |
| Name Other: | Martonka-patak |
| Pushpin Map: | Romania |
| Subdivision Type1: | Country |
| Subdivision Name1: | Romania |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Harghita County |
| Subdivision Type3: | Villages |
| Subdivision Name3: | Făgețel, Martonca |
| Length: | 14km (09miles) |
| Source1: | Gurghiu Mountains |
| Mouth: | Mureș |
| Mouth Coordinates: | 46.8487°N 25.4486°W |
| Basin Size: | 24km2 |
| Tributaries Right: | Lucaci |
The Martonca (Hungarian: Martonka-patak, from the name "Martin") is a left tributary of the river Mureș in Transylvania, Romania. It discharges into the Mureș near Subcetate. Its length is 14km (09miles) and its basin size is 24km2.