[2] Microryzomys species are small members of the rodent tribe Oryzomyini, weighing in the region of 10 to 15 g (0.35 to 0.53 oz), and characterised by their long soft fur and tail longer than their head-and-body-length.

They have small hind feet with six fleshy pads on the under surface, and with the fifth toe nearly as long as the middle three.

[3] At one time, this genus was considered to be a subgenus of Oryzomys, but Carleton and Musser (1989) raised it to full generic status on the basis of various anatomic details of skull and dentition and on certain morphological traits.

[4] Microryzomys is found in high mountainous areas of western South America.

M. minutus mostly occurs in moist forest habitats at altitudes between 1,500 and 3,500 m (4,900 and 11,500 ft), while M. altissimus inhabits moist subalpine forests and páramo grassland, at altitudes between 2,500 and 4,000 m (8,200 and 13,100 ft).