Lostallo is a municipality in the Moesa Region in the Swiss canton of the Grisons .

Lostallo is first mentioned in 1219.

Lostallo has an area, as of 2006, of 50.9 km2 (19.7 sq mi). Of this area, 6.8% is used for agricultural purposes, while 59% is forested. Of the rest of the land, 1.8% is settled (buildings or roads) and the remainder (32.3%) is non-productive (rivers, glaciers or mountains).

Before 2017, the municipality was located in the Mesocco sub-district of the Moesa district on the right bank of the Moesa river.