Abstract: Objective To observe the effect of ornidazole carboxymethyl chitosan combined with hyaluronic acid as an auxiliary means for periodontal initial therapy in treating elderly patients with chronic periodontitis. Methods Totally 112 elderly patients with chronic periodontitis were selected and randomly divided into observation group and controlgroup, with 56 cases in each group. All patients were treated with periodontal initial therapy, the control group was injected with hyaluronic acid from the bottom of periodontal bag after operation, and the observation group was injected with ornidazole carboxymethyl chitosan combined with hyaluronic acid into the bottom of periodontal bag. The clinical efficacy, periodontal indexes, the level of trypsin like enzyme(TLE)and the ratio of spirochetes(S%)were compared between the two groups before and after 28 days of treatment. Results After 28 days of treatment, the levels of attachment loss(AL), bleeding index(BI), plaque index(PLI)and probe depth(PD)in both groups were significantly lower than those before treatment, and those in the observation group were significantly lower than the control group(P<0.05). After 28 days of treatment, the values of TLE and S% in both groups were significantly lower than those before treatment, and those in the observation group were significantly lower than the control group(P<0.05). The total effective rate of the observation group was 92.86%, which was significantly higher than 78.57% of the control group(P<0.05). Conclusion Ornidazole carboxymethyl - chitosan combined with hyaluronic acid as an auxiliary means for periodontal initial therapy is effective in the treatment of elderly patients with chronic periodontitis, which can improve the level of periodontal related indicators, reduce the level of TLE and the number of spirochetes in subgingival plaque.