The Little River National Wildlife Refuge (6,070 ha) is located on the west Gulf Coastal Plain in southeastern Oklahoma, a region of high plant diversity for the state. An inventory of the refuge yielded 708 taxa of vascular plants in 688 species, 410 genera, and 128 families. The largest families were the Asteraceae (n = 88 taxa), Poaceae (n = 76), Cyperaceae (n = 49), and Fabaceae (n = 44). Sixty-seven nonnative taxa were collected, representing 9.5% of the flora. Sixty-two taxa were present that are tracked by the Oklahoma Natural Heritage Inventory, including the Oklahoma endemic, Leavenworthia aurea var. aurea. In addition, we report the first Oklahoma collection of Polygonum glabrum.