Abstract： Objective To evaluate the effect of concentration of chlorhexidine on bonding durability of dentine and resin. Methods Forty extracted third molars were randomly allocated into five groups, which include one control group and four test groups. Teeth dentin surfaces in each group were treated with one of the following solution, 1.5 μl water(control), 0. 02%, 0. 2%, 2% and 20% chlorhexidine. Single Bond 2 adhesive was applied to the dentin surface according to manufacturer's recommendations. Then 5 mm thickness of composite (Z250) was built up on the dentin of each molar. The teeth were sectioned into mierotensile samples and subdivided into two subgroups, 16 samples each. Samples in subgroup Ⅱ and Ⅰ were tested after being stored in distilled water for 24 h and 6 month respectively. Each fractured sample was examined with SEM. Results No significant differences of 24 h bonding strength were found among the five groups. There were significant difference in bonding strength between 0. 2%, 2% chlorhexidine groups [(24. 68±5. 26) and (23. 19±5. 26) MPa]and the control group[(19. 10±4. 67) MPa]after 6 month (P = 0. 007,0. 045), and significant differences were also found between 0. 2%, 2% and 0. 02% ehlorhexidine group[(19.01 ±6. 87) MPa, P =0. 006, 0. 041). Most of the fractured modes were mixed or interface failures after 24 h of water storage, and the mixed failure increased after six month of water storage. In the 0. 2%, 2% and 20% chlorhexidine treated group, most of the failure was found at the top of hybrid layer, while in the 0. 02% group, it was found in the base part of hybrid layer. Conclusions Chlorhexidine could increase the bonding durability of resin and dentine. Higher than 0. 2%, concentration of chlorhexidine couldn't improve bonding durability.