The Sao Paulo grass mouse is a small rodent with dark fur over the body. It is known from only four sites in Sao Paulo state, southeastern Brazil, and little is known about its natural history.
It is medium-sized for Akodon, with a head-and-body length of 73–100 mm and a tail of 58–75 mm. Its dorsal, flank, and ventral fur are all very dark; the tail is weakly bicolored, and hairs on the feet have dark bases and white tips.
Its ecology is little known. The few recorded localities lie in a remaining area of dense montane and submontane evergreen forest in the Atlantic Forest of coastal Brazil.
An extinction-risk assessment has not been added yet.