The Pawcatuck River is a short river in the northeastern United States, approximately 30 mi/48 km long. It forms part of the boundary between the states of Connecticut (to the west) and Rhode Island to the east, emptying into Rhode Island Sound. The river was specificied as the western boundary of the Rhode Island Colony in its original charter in 1636. The river was formerly called "Charles River" between its source and the mouth of Wood River near Bradford, Rhode Island.

It rises in southern Rhode Island in Worden Pond, then flows west and southeast past Kenyon , Carolina , and Bradford. It then turns briefly northwest and west before resuming a southwarward course to flow past Potter Hill and between the towns of Westerly, Rhode Island and Pawcatuck, Connecticut. It empties into Little Narragansett Bay on Rhode Island Sound approximately 13 mi/21 km east of New London, Connecticut.