Objective: To study the agreement and reproducibility of probing depth(PD) measurements between the electronic computerized periodontal probe for constant pressure and the conventional manual periodontal probe before mechanical treatment in patients with chronic peridodontitis. Methods:PD values of total 144 periodontal sites from 12 patients with chronic periodontitis were duplicately measured using electronic periodontal probe and conventional manual probe before instrumental therapy by two examiners at two visits for the 1st day and the 7th day, respectively, Analysis of the agreement by intraclass correlation coefficient (ICC) and reproducibility between the two different periodontal probes on PD measurement was performed by paired t-test. Different examiners,different visits time, different periodontal pocket depth, different probes(methods) were taken into consideration as possible factors leading to the difference. Results:The agreement and reproduciblity of PD values from two different probes were good (P > 0.05)both between two examiners and two visits. In addition, by linear regression model the difference of PD values between two tools is contributed to the periodontal pocket depth(t=72.42,P<0.001) other than examiners(t=0.26,P=0.793),visits(t=-0.17,P=0.866)or periodontal probes(t=-0.44,P=0.662). Conclusion: Electronic periodontal probe and manual periodontal probe, which are used by examiners trained normally and strictly, are both reliable tools for pretreatment measuring PD values in chronic peridodontitis.