Objective：To research the effects of diabetes on periodontitis model in rats. Methods：The animal model of periodontitis was established by ligating the right maxillary first molar of 48 male SD rats（6 weeks，160-180 g） through stainless steel wire. All rats were divided into two groups randomly：periodontitis combined with diabetes（G1）group and periodontitis（G2） group. Diabete’s models were established by injecting streptozocin intraperitoneally. Six rats were killed in each group after 1，2，3，4 weeks. Sulcus bleeding index（SBI），probing depth（PD）and alveolar bone loss（ABL） were measured. Periodontal histology was observed by micro－scope. Interleukin-1β（IL-1β） and tumor nectosis factor-α（TNF-α） levels were analyzed by immunohistochemistry. Results：（1）At the same time，SBI，PD，ABL were higher in G1 group than in G2 group with statistical significances（P<0.05）；（2）The inflammations of periodontal histology were more serious in G1 group than in G2 group；（3）At the same time，IL-1β and TNF-α levels were higher in G1 group than in G2 group（P<0.05）. Conclusion：Under the experiment condition，diabetes can aggravate the rat periodontitis.