Abstract：Objective：To observe the clinical effect of modified Bazhen tang assisting western medicine for chronic periodontitis. Methods：A total of 136 cases of patients with chronic periodontitis were selected and divided into the control group and the observation group according to the random number table method， with 68 cases in each group. Both groups were given oral hygiene instruction and periodontal basic treatment. After being given periodontal basic treatment，the control group was additionally given the oral administration of metronidazole tablets， and the observation group was additionally given the oral administration of modified Bazhen tang based on the treatment of the control group. The clinical effects in the two groups were evaluated； the periodontal indexes including plaque index(PLI)， periodontal pocket depth(PD)，gingival index(GI) and attachment loss(AL)，Chinese medicine symptom scores and incidences of adverse reactions in the two groups were compared. Results：The total effective rate was 91.18% in the observation group， higher than that of 77.94% in the control group， the difference being significant(P＜ 0.05). Before treatment，there was no significant difference being found in the comparison of PLI，PD，GI and AL between the two groups(P＞0.05). After treatment，PLI，PD，GI and AL in the two groups were decreased when compared with those before treatment，and PLI，PD，GI and AL in the observation group were lower than those in the control group，differences being significant(P＜0.05). Before treatment，there was no significant difference being found in the comparison of the scores of gingival redness and swelling， gingival bleeding， tooth mobility and halitosis between the two groups(P＞0.05). After treatment， the scores of gingival redness and swelling，gingival bleeding，tooth mobility and halitosis in the two groups were decreased when compared with those before treatment， and the above scores in the observation group were lower than those in the control group， differences being significant(P＜0.05). The total incidence of adverse reactions was 4.41% in the observation group， lower than that of 17.65% in the control group，the difference being significant(P＜0.05). Conclusion：The therapy of modified Bazhen tang assisting western medicine for chronic periodontitis can significantly improve periodontal indexes，reduce clinical symptoms with few adverse reactions.