Nephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica.

[1] Its generic name is derived from the Ancient Greek word nephelê "mist", referring to the cloud forest habitat of the members of the genus.

[5] Oryzomys appears in a different part of the oryzomyine evolutionary radiation, perhaps close to Holochilus and related genera.

The ears are small, but the tail is long, and it is bicolored to a smaller or greater extent, depending on the species.

[6] Weksler and coworkers provided detailed comparisons among Euryoryzomys, Hylaeamys, Nephelomys, and Transandinomys.