| South Branch Little Dead Diamond 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: | Coos |
| Subdivision Type4: | Townships |
| Subdivision Name4: | Dix's Grant, Clarksville, Atkinson & Gilmanton Grant, Second College Grant |
| Length: | 4.3miles |
| Source1: | Crystal Mountain |
| Source1 Location: | Dix's Grant |
| Source1 Coordinates: | 44.9511°N -71.2072°W |
| Source1 Elevation: | 2760feet |
| Mouth: | Little Dead Diamond River |
| Mouth Location: | Second College Grant |
| Mouth Coordinates: | 44.9658°N -71.1419°W |
| Mouth Elevation: | 1560feet |
| Tributaries Right: | Lost Valley Brook |
The South Branch of the Little Dead Diamond River is a 4.3adj=midNaNadj=mid[1] river in northern New Hampshire in the United States. It is a tributary of the Little Dead Diamond River, located in the Androscoggin River watershed of Maine and New Hampshire.
The river rises in the township of Dix's Grant on the eastern slopes of Crystal Mountain, a 7adj=midNaNadj=mid ridge. The river flows northeast into the Atkinson and Gilmanton Academy Grant, then joins the Little Dead Diamond in the Dartmouth College Grant.