| Nissitissit River | |
| Pushpin Map: | New Hampshire#Massachusetts#USA |
| Pushpin Map Size: | 250 px |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | States |
| Subdivision Name2: | New Hampshire, Massachusetts |
| Subdivision Type3: | Counties |
| Subdivision Name3: | Hillsborough, NH, Middlesex, MA |
| Subdivision Type4: | Towns |
| Subdivision Name4: | Brookline & Hollis, NH; Pepperell, MA |
| Length: | 10.5miles |
| Source1: | Potanipo Pond |
| Source1 Location: | Brookline, NH |
| Source1 Coordinates: | 42.7361°N -71.6722°W |
| Source1 Elevation: | 80.5order=flipNaNorder=flip |
| Mouth: | Nashua River |
| Mouth Location: | Pepperell, MA |
| Mouth Coordinates: | 42.6717°N -71.5647°W |
| Mouth Elevation: | 168feet |
The Nissitissit River is a 10.5adj=midNaNadj=mid[1] river in southern New Hampshire and northern Massachusetts in the United States. It is a tributary of the Nashua River, itself a tributary of the Merrimack River, which flows to the Gulf of Maine. This river is part of the Nashua River Watershed.
The Nissitissit River begins at the outlet of Potanipo Pond in the town of Brookline, New Hampshire. It flows southeast at a very mild gradient, crossing the southwest corner of Hollis, New Hampshire, before entering Massachusetts, where it joins the Nashua River in the town of Pepperell.