Phaeoacremonium is a recently described genus (Crous et al. 1996) associated with decline diseases of woody hosts and with human infections. During a study of surface mycobiota of the oak bark beetles, the hyphomycetous microfungus Phaeoacremonium rubrigenum was isolated from larvae of Scolytus intricatus (Coleoptera: Scolytidae) and their galleries on Quercus robur and also from an adult of Leperisinus fraxini found under the bark of Fraxinus excelsior. The species determination was confirmed by rDNA (ITS1-5.8S-ITS2) comparison. P. rubrigenum was recorded for the first time in Czechia. The records on oak are considered to be the first ones in the world. A description of morphological features and figures of the fungus are given. Representative strains are maintained in the Culture Collection of Fungi (CCF), Faculty of Science, Charles University (Prague, Czechia).