Route 138 is a major highway in the Canadian province of Quebec, following the entire north shore of the Saint Lawrence River past Montreal to the temporary eastern terminus in Kegashka on the Gulf of Saint Lawrence. The western terminus is in Elgin, at the border with New York State south-west of Montreal. Part of this highway is known as the Chemin du Roy, or King's Highway, which is one of the oldest highways in Canada.

Kegaska, population 138, is the easternmost point in the Côte-Nord region of Quebec, Canada to be reachable by road without passing through Newfoundland and Labrador. Quebec Route 138 reached the community on September 26, 2013, with the inauguration of a bridge across the Natashquan River.