The white-bellied nesomys has ventral hairs that are white to their bases. In a Madagascar field study, the animals were also active during daylight.
The white ventral hairs extend to their bases; short white hairs at the tail tip are present in some individuals.
Animals studied in Ranomafana National Park in 1987–1989 were active during daylight. The forest study site lay on a ridge at 900–1,000 m elevation.
In the Ranomafana sample, this species was heavier and had longer hind feet than Nesomys rufus. Mean hindfoot length was 54.6 mm in N. audeberti and 49 mm in N. rufus.
In the two examined specimens from the original type series, the tail hairs were short, leaving the scales visible over most of the tail.
An extinction-risk assessment has not been added yet.