Objective:To evaluate the clinical effect of a set of nickel-titanium rotary instruments,named ProTaper,in preparing curved root canals of the aged. Methods:Eighty-two posterior teeth of aged people with curved root canals were randomly divided into two groups. The 41 teeth in experiment group were managed by ProTaper nickel-titanium rotary instruments using crown-down technique;while the 41 teeth in control group by stainless steel K files. All teeth were obturated with lateral condensation method. The effects of preparation and obturation with radiographs before,during and after operation were analyzed. Results:Compared with the control group,the nickel-titanium rotary instruments kept the curvature and flow of curved canals very well,and the continuously tapered root canal shape was achieved in all cases. The time of operation was short and endodontic flare-up seldom occurred. However,the test group had two fractured files. Conclusion:The ProTaper nickel-titanium rotary instruments can prepare curved root canals effectively and quickly. Meanwhile,the problem of instrument separation due to many reasons such as variations in canal anatomy and fatigue of instruments should be prevented.