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

Grengiols is first mentioned in 1052 as Graneirolis. In 1228 it was mentioned as Griniruel and in 1297 as Graniols. The name probably comes from the Latin word graneirolas meaning a small granary.

Grengiols has an area, as of 2011, of 58.5 square kilometers (22.6 sq mi). Of this area, 21.2% is used for agricultural purposes, while 25.6% is forested.