The rivière du Moulin (in English: Mill River) is a tributary of the south shore of the St. Lawrence River.

This river flows in the area of Gentilly of the town of Bécancour, in the Bécancour Regional County Municipality, in the administrative region of Centre-du-Québec, in Quebec, in Canada.

From its head area, the Moulin river flows over 9.6 kilometres (6.0 mi) with a drop of 33 metres (108 ft), divided into the following segments: The Rivière du Moulin flows onto the south shore of the St. Lawrence River, in the eastern part of the territory of the town of Bécancour, that is to say to the northeast of the village of Gentilly.

Its confluence is located east of the village of Gentilly and 2.4 kilometres (1.5 mi) west of the confluence of the Orignaux river (Gentilly) and 2.1 kilometres (1.3 mi) at west of the confluence of the Rivière aux Glaises.

The toponym Rivière du Moulin was made official on December 5, 1968, at the Commission de toponymie du Québec.