Ucucha's thomasomys is a small rodent studied in the highlands of eastern Ecuador. Near Papallacta, specimens were collected at elevations of 3,380–3,720 m.
The back fur is dense, fine, and soft, about 13–15 mm long. It ranges from brownish olive on the flanks to dark grayish brown along the middle of the back, without a sharp boundary from the underside.
Most of 42 specimens collected near Papallacta were caught on the ground, in runways through grass or low herbs, among moss or damp litter, and along small streams.
An extinction-risk assessment has not been added yet.