The limbs are usually buffy gray, and the hands and feet are buffy gray or brownish white. The tail is thinly haired and sometimes penciled terminally. The vibrissae are prominent and slightly longer than the head. The hind feet are specialized for arboreal life in that they have enlarged toe pads consisting of two flat plates with a groove between them. The general body form of Hapalomys is ratlike.
Females have eight mammae.
The incisor teeth are broadened and powerful. Hapalomys is the only murid genus with three rows of approximately equally developed cusps on the lower cheek teeth, a character that some authorities consider to be very primitive. These mice are arboreal and inhabit tropical forests. By day it retires to a nest in the internodal cavities of dead or living bamboo stems. It gains access to the internodes by gnawing a circular hole about 35 mm in diameter in the outer wall.