A study of the vegetation of Dean Hills Nature Preserve in Fayette County, Illinois was undertaken to document the composition and structure of the vascular flora and to provide information for land management decisions. A total of 313 species in 85 families and 204 genera were collected at the 30-hectare preserve which occurs on a glacial kame and has a rugged ridge and ravine topography. Mature mesic and dry-mesic forest covers much of the preserve. The canopy is dominated by white oak (Quercus alba), red oak (Quercus rubra), and sugar maple (Acer saccharum). Data suggest that sugar maple is regenerating more successfully than the oaks. This same result has been found in several other studies of oak-hickory forests in Illinois. If management such as prescribed burning is not implemented, it is predicted that sugar maple will increase and oaks will decrease in dominance within the preserve.