Abstract: PURPOSE To investigate the impact of S.gordonii on the ultrastructure of P. gingivalis biofilm and on the amount of P. gingivalis in biofilm. METHODS P. gingivalis and/or S.gordonii grew on the culture slides to form single P. gingivalis biofilm and heterotypic biofilm of P.gingivalis-S.gordonii. Then the ultrastructure of the 2 kinds of film were examined by scanning electron microscope, and the amount of P. gingivalis in the biofilm was detected by qPCR. Statistical analysis was performed using pair t test with SPSS 13.0 statistical package. RESULTS At 72 h, the amount of heterotypic biofilm was much more than that of the single P. gingivalis biofilm. Moreover, the structure of the heterotypic biofilm was more regular and with more pore space compared to the single P. gingivalis biofilm. Compared to single P. gingivalis biofilm, the amount of P. gingivalis in heterotypic biofilm was 5.4, 3.8 and 4.4 fold at 24, 48 and 72 h, respectively.CONCLUSIONS The growth of P. gingivalis was promoted by S. gordonii in the form of heterotypic biofilm compared to single P. gingivalis biofilm.