Unterbäch is a municipality in the district of West Raron in the canton of Valais in Switzerland .

Unterbäch is first mentioned about 1280 as Underbechque. On 18 August 1957, Unterbäch was the first community in Switzerland to establish the communal voting and election rights for women.

Unterbäch has an area, as of 2011, of 22 square kilometers (8.5 sq mi). Of this area, 27.7% is used for agricultural purposes, while 27.7% is forested. Of the rest of the land, 1.6% is settled (buildings or roads) and 43.0% is unproductive land.