Abstract: Results of studies on diversity of arthropod-pathogenic fungi in selected habitats in Austria and Poland carried out in the years 2006-2007 and 2009-2010 are discussed. In total 47 species of entomopathogenic fungi were found as pathogens of different arthropods in Austria. Twenty six entomophthoralean species from different insects and one species from mites were identified and 16 of them are recorded as new to Austria. From among 21 species of anamorphic Hypocreales (Ascomycota) affecting arthropods in Austria, 13 species so far have not been known from this country. In total 51 species of fungi affecting different arthropods in Poland were recorded, among them 28 species of Entomophthorales and 23 anamorphic Hypocreales (Ascomycota) were separated. The most frequent species of the entomopathogenic fungi both in agricultural and afforested areas in Austria were the common and usually worldwide distributed cordycipitaceous anamorphs Beauveria bassiana, Isaria fumosorosea and in areas of this study less numerous I. farinosa . The most frequent pathogens occurring in mite communities on plants and in wood infested by insects were Hirsutella species. Several entomophthoralean species developed epizootics that caused high reduction in host populations of different arthropods in both countries. Especially interesting is the first record of mycoses (up to 60% mortality), caused by Zoophthora spp. on Phyllobius beetles in a mixed forest near Bialowieza. During our joint research, we found the first time in Poland and Europe, the presence of the fungus Furia cf. shandongensis on earwigs and Hirsutella entomophila on Ips typographus adults in forest habitats. From the feeding sites of the latter bark beetle and other subcortical species in oak bark (mostly Dryocoetes villosus ) and D. alni in black alder over a dozen of various Lecanicillium strains - including few of the features not allowing to classify them to any of so far known species – were isolated both from the scolytids and from accompanying them mites, but these materials have now been successively elaborated. From the commonly occurring in these materials acaropathogenic species Hirsutella cf. brownorum, H. minnesotensis, H. nodulosa and H. rostrata , the two latter infected also adult bark beetles, whereas from the larvae and pupae some supposed nematophagous anamorphs were isolated, among them Harposporium janus and Haptocillium sp.