Cockroaches are worldwide indoor pests carrying microorganisms of medical importance.German cockroaches(Blattella germanica) were sampled in five habitats(hospital,restaurant,offce home,and market) in Beijing,and the bacteria were isolated from their external surface and alimentary tract and identified using a Biolog identification system.Cockroach densities significantly differed among habitats(market > home > offce > restaurant > hospital).However,no significant differences in bacterial abundance carried by individual German cockroaches(of either sex) were found among habitats.The bacterial abundance in the gut was significantly higher than that on the surface.There were no significant differences in bacterial species richness observed among habitats,sex,carrying position or their interaction.Cluster analysis showed that cockroach densities and bacterial abundance found in the market differed significantly from the other four habitats.The bacterial diversity was not significantly reduced in sensitive facilities such as hospital and restaurant,even though pesticide and bactericide were more frequently applied there.The implications of these findings were discussed in this article. Cockroaches are worldwide indoor pests carrying microorganisms of medical importance. German cockroaches (Blattella germanica) were sampled in five habitats (hospital, restaurant, offce home, and market) in Beijing, and the bacteria were isolated from their external surface and alimentary tract and identified using a Biolog identification system. Cockroach densities significantly differed among habitats (home> offce> restaurant> hospital) .However, no significant differences in bacterial abundance carried by individual German cockroaches (of either sex) were found among habitats. The bacterial abundance in the gut was significantly higher than that on the surface. where were no significant differences in bacterial species richness observed among habitats, sex, carrying position or their interaction. Cluster analysis showed that cockroach densities and bacterial abundance found in the market differed significantly from the other four habitats.The bacterial diversity was not significantly red uced in sensitive facilities such as hospital and restaurant, even though pesticide and bactericide were more frequently applied there.The implications of these findings were discussed in this article.