straw-colored pygmy rice rat

Oligoryzomys stramineus is a large species of colilargo with a yellowish-brown head and dorsal surface and whitish underparts, with a sharp line demarcating the boundary between the two. It has long incisive foramina (openings in the hard palate of the skull) and broad zygomatic plates (bony plates in the upper jaw). The head-and-body length averages 94 mm (3.70 in) while the tail averages 118 mm (4.65 in).

This species is native to South America where it occurs in northeastern and central Brazil. Its range extends from the cerrado ecoregion of the states of northern Goiás and northern Minas Gerais southward to the caatinga ecoregion of the states of Paraíba and Pernambuco. In the cerrado, it has mainly been found in gallery forests. It shares part of its range in central Brazil with Oligoryzomys fornesi and is sometimes caught in the same line of traps. It is also sympatric with Oligoryzomys nigripes, but the two species are not found in the same trap-lines.

Little is known of the breeding habits of O. stramineus; a pregnant female carrying four young was caught in September; and a juvenile was caught in August suggesting that mating may have occurred in June or July.