Anti-Beauveria bassiana activity of aqueous fecal extracts from conventional German cockroaches [Blattella germanica (L.)] was detected, but was not detected in samples from germ-free German cockroaches. Subsequently, bacterial strain BGI-14 was isolated from the gut of conventional German cockroaches and was identified as Pseudomonas reactans based on 16S rDNA sequence. The strain BGI-14 not only inhibited the germination of conidia, but also inhibited the growth of B. bassiana hyphae. Further studies demonstrated that B. bassiana infections in German cockroaches orally treated with the extracts of BGI-14 fermentation were significantly weakened. Compared with the control group, the cumulative mortality rate of treatment group was reduced by 10.3% at 20 d postinoculation. These studies imply that intestinal flora with anti-B. bassiana activity might contribute to resistance of infection by entomopathogenic fungi.