Rio Grande Cooters (Pseudemys gorzugi) are one of the least studied species of freshwater turtles in North America. Rio Grande Cooters are listed as a state threatened species in New Mexico and near threatened by the International Union for Conservation of Nature. Given their conservation status, it is important to understand the natural history of this species. We conducted the first in-depth investigation of the dietary habits of P. gorzugi at two sites within the Black River in Eddy County, New Mexico, USA, by using fecal sample analyses. We captured and attempted to collect fecal samples from 277 turtles (205 nonrecapture, 72 recapture) and successfully collected 78 samples. Fecal content analysis revealed vegetation including netleaf hackberry (Celtis reticulata), cottonwood (Populus sp.), willow (Salix sp.), monocot grasses, and filamentous algae, along with animals including nine orders of insects, a crustacean, a feather, a fish vertebra, and monofilament fishing line. We found that turtle diets were omnivorous to varying degrees between sexes. Dicot vegetation, filamentous algae, and arthropods were found to be the most important diet components in male (index of relative importance [IRI] = 0.47), female (IRI = 0.53), and juvenile (IRI = 0.63) P. gorzugi, respectively. Juveniles were found to have a more specialized diet or lesser dietary breadth compared with diets of adult males and females. Future studies should investigate the nutritional value and digestibility of dietary resources, interspecific competition, and comparison of diet of P. gorzugi from different river systems.