The Red Slough Wildlife Management Area (7,800 ha) is located on the West Gulf Coastal Plain in southeastern Oklahoma. The inventory was motivated by land acquisitions and is intended to augment a 1999 inventory. We report an additional 202 taxa of vascular plants, with 186 species, 16 infraspecific taxa, 158 genera, and 68 families. This is a 62% increase in the number of taxa previously listed for the site. The largest families were the Poaceae (with 35 taxa), Asteraceae (20 taxa), and Fabaceae (18 taxa). Thirty-one nonnative taxa and 19 taxa tracked by the Oklahoma Natural Heritage Inventory were encountered.