Abstract: [Abstract] Objective To evaluate clinical effect of calcium hydroxide in controlling the EIAP. Methods 386 cases, which were diagnosed as pulpitis and periapical periodontitis with EIAP were selected. They were randomly divided into experimental group (calcium hydroxide) and control group (camphor phenol+ iodoform) with 193 cases in each group. The materials were inserted into the canal root and then to observe whether the EIAP was eliminated after using material in root canal. Results The success rate of mild and moderate cases in experimental group was 92.8% and 94.4% respectively, significantly better than the 82.3% and 65.2% in the control group（P＜0.01). There were no differences between the groups of patients with severe pain(P＞0.05).Conclusions Calcium hydroxide paste is an ideal root canal disinfectant, which can control the EIAP effectively.