The Upper Ammonoosuc River is a tributary of the Connecticut River that flows through Coös County in the northern part of the northeastern U.S. state of New Hampshire.

The Upper Ammonoosuc rises in Pond of Safety in the town of Randolph, runs first generally north through rural portions of Berlin (where it flows through the Godfrey Dam), Milan and a corner of Dummer, then west through Stark and then Northumberland, where it drains into the Connecticut near the village of Groveton.

[1] From Milan to Groveton it is fairly closely paralleled by New Hampshire Route 110.

Fort Wentworth was built in 1755 at the junction of the Upper Ammonoosuc and Connecticut rivers (now near the village of Groveton).

Major tributaries of the Upper Ammonoosuc include: