Objective The study is to investigate the microbial composition of interdental and subgingival plaques of periodon- titis patientswith orwithoutmalodor, to explore the relationships between periodontitis and oral malodor.Methods 20 patients of periodontitis with malodor were chosen from 210 patients of periodontitis, and the clinical parameter of plaque index (PLI), gingi- val bleeding index (GBI) and probing depth (PD) were measured and compared with the control groupwhich had periodontal dis- ease without malodor. During the experiment, the interdental and subgingival microbial samples in both groups were collected and sent to anaerobic culture for 48 hrs, then the total CFU/ml of each sample were counted, and each type of bacteria was separated and identified. All of the data were analyzed by using the statistical software SPSS 10.0.Results (1)There were no satistical differences on PLI, GBI, PD between experimental group and control group. (2) The percents of leptospira in both interdental and subgingival plaques of test groupwere significantly higherthan that of the control group (P0.05). (4) The proportions of malodor pro- ducing anaerobic bacteria in interdental gingival plaque, such asP.gingivalisandVeillonella, were singnificantly different be- tween test group and control group.Conclusion The proportions of VSC′s producing anaerobic bacteria in interdental gingival plaque may be play the significant roles in oral malodor. Further studies should be taken to elucidate the relationship between mal- odor and periodontitis.