| Official Name: | Rahnishk |
| Native Name: | رهنیشک |
| Settlement Type: | village |
| Pushpin Map: | Iran |
| Mapsize: | 150px |
| Subdivision Type: | Country |
| Subdivision Type1: | Province |
| Subdivision Name1: | South Khorasan |
| Subdivision Type2: | County |
| Subdivision Name2: | Birjand |
| Subdivision Type3: | Bakhsh |
| Subdivision Name3: | Central |
| Subdivision Type4: | Rural District |
| Subdivision Name4: | Kahshang |
| Population As Of: | 2016 |
| Population Total: | 82 |
| Population Density Km2: | auto |
| Timezone: | IRST |
| Utc Offset: | +3:30 |
| Timezone Dst: | IRDT |
| Utc Offset Dst: | +4:30 |
| Coordinates: | 32.9611°N 59.4603°W |
Rahnishk (Persian: رهنیشک, also Romanized as Rahnīshk, Rahanīshk, and Rahneshk; also known as Rahneg and Ranishk) is a village in Kahshang Rural District, in the Central District of Birjand County, South Khorasan Province, Iran. At the 2016 census, its population was 82, in 28 families.