An outbreak of red oak borer, Enaphalodes rufulus (Haldeman), in Arkansas has resulted in millions of dollars in damage to oak trees. A survey for microbial pathogens of late stages of red oak borer in northwest Arkansas forests demonstrated that red oak borer infected with Beauveria bassiana were present in 12 of 21 Quercus spp. trees. Oak trees dissected in the survey were located in an area of heavy infestation in the Ozark National Forest, Franklin County, Arkansas. Individual trees were selected for the survey based on a likelihood of E. rufulus infestation. Overall prevalence of B. bassiana-infection was 2.7%. Infected late stage larvae, pupae and adults were found between May and July 2003. Mean number of late stage larval, pupal and adult red oak borers per 0.5 m bole sample was 1.64 (SE ± 0.1). Mean number of B. bassiana-infected red oak borer per 0.5 m bole sample was 0.04 (SE ± 0.01). These data demonstrate that B. bassiana-infected red oak borers in Quercus spp. were found throughout the height of the tree.