The mountain Sundamys is a large rat of montane forest in Borneo and western Sumatra. Plant shoots and twigs have been recorded in its diet.
The upper fur is blackish brown; the underside is dark gray and may have an orange tinge. Its long tail is dark.
It lives in montane primary forest. Shoots, twigs, and bark have been recorded as food, and it is presumed to be nocturnal.
An extinction-risk assessment has not been added yet.