The South Branch of the Little Dead Diamond River is a 4.3 mi 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 7 mi ridge. The river flows northeast into the Atkinson and Gilmanton Academy Grant, then joins the Little Dead Diamond in the Dartmouth College Grant.