After morphological and karyological analysis, we identificated 12 specimens of the Straw Colored Pigmy Rice Rat, Oligoryzomys stramineus (Bonvicino and Weksler, 1998) in northeastern Brazil. Karyotypic analysis showed 2n=52, FNa=68, with 9 biarmed and 16 acrocentric autosome pairs, similar to those reported for O. stramineus in others studies. Pregnant females were captured during the wet season, corroborating that the reproductive period is not restricted to the dry season. We report the northernmost record for O. stramineus in Russas municipality (04°56’25” S, 37°58’33” W), state of Ceará, Brazil, located in the Caatinga domain, extending the range of the species ca. 330 km N. Together with the record from Salenópolis municipality (07°18’33” S, 39°73’33” W), they are the first records of O. stramineus in Ceará.