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. Of the rest of the land, 0.8% is settled (buildings or roads) and 52.4% is unproductive land.
The municipality is located in the Östlich Raron district, on the southern slopes of the Rhone valley near the entrance to the Goms valley. It consists of the village of Grengiols with scattered settlements including; Hockmatte, Ze Hyschere, Bächerhyschere and others, on the road leading into the Goms valley and then over the Albrun Pass.
The blazon of the municipal coat of arms is Gules, two Keys Or in saltire in chief a papal Crown of the same.