Bombus monticola is a species of medium-small size.
Females: 15-28 mm
Males: 12-15 mm
The head has yellow and black mixed hairiness. Black torax, with yellow collar and scutellum. T1 sides are yellow, and the centre is black. T2 is black in its anterior half. The rest of the gaster is red ferruginous. Males have similar coloration, but the yellow colour is more widespread.