So we chose to focus on a native common dioecious plants from northern China , Populus cathayana Rehd and used 16S rRNA gene-based pyrosequencing methods to characterize and compare the relative abundance, the composition and diversity of phyllosphere bacteria and fungi between Populus cathayana. females and males. Previous studies revealed that the distinction between endophytic and epiphytic fungal species is ambiguous, because some epiphytic fungi also actively penetrate the epidermis or stomata and colonize internal leaf tissues (Viret and Petrini 1994). In this study, we define phyllosphere bacteria and fungi as those species inhabiting both the surface and the interior of leaves(Jumpponen and Jones 2009). The main objectives were to determine whether there are differences about fungal and bacterial communities between females and males, and to examine whether the phyllosphere microbial biodiversity is related to leaf physicochemical properties. Our results could provide insights into relationships between phyllosphere microbial biodiversity and dioecious plants.