Thomasomys praetor is a rodent from the mountains of northwestern Peru. Specimen records include páramo scrub and the timberline of dry forests in the Marañón Valley.
Its long, soft dorsal fur is gray-olive and darker along the middle and rear of the back. The head, cheeks, and sides are yellowish gray; the belly is buffy white.
Peruvian specimens were collected in páramo scrub, timberline shrubs, and dense vegetation on rocky ground. Some records are from sites near rivers or streams.
An extinction-risk assessment has not been added yet.