On all four limbs the first four digits are well developed and have sharp claws, but the fifth is reduced. Long, comblike bristles extend over the claws of the hind feet. The auditory bullae are moderate in size and smaller than those of Octodontomys and Octomys. The anterior upper cheek teeth of O. degus are kidney-shaped, with only moderate internal indentations. The incisor enamel is pale orange.
Females have eight mammae.
This species inhabits the west slope of the Andes at elevations of up to 1,200 meters. It is found in relatively open areas near thickets, rocks, or stone walls. It is active throughout the year and is diurnal, with peaks of activity in the morning and late afternoon. It feeds on the ground and will also climb into the branches of small trees and bushes. An elaborate communal burrow system is constructed, with the main section under rocks or shrubs.