| Rattlesnake River | |
| Pushpin Map: | New Hampshire#USA |
| Pushpin Map Size: | 250 px |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | New Hampshire |
| Subdivision Type3: | County |
| Subdivision Name3: | Strafford |
| Subdivision Type4: | Towns |
| Subdivision Name4: | Farmington |
| Length: | 3.6miles |
| Source1 Location: | Farmington |
| Source1 Coordinates: | 43.3569°N -71.0806°W |
| Source1 Elevation: | 710feet |
| Mouth: | Cocheco River |
| Mouth Location: | Farmington |
| Mouth Coordinates: | 43.3664°N -71.0361°W |
| Mouth Elevation: | 238feet |
The Rattlesnake River is a 3.6adj=midNaNadj=mid[1] river in eastern New Hampshire in the United States. It is a tributary of the Cocheco River, part of the Piscataqua River watershed leading to the Atlantic Ocean.
The river is located entirely in the town of Farmington. It rises north of Hussey Mountain and Chesley Mountain and flows east to the Cocheco, dropping nearly in elevation over its length.