Objective:To compare the cleaning effectiveness of rotary Protaper and stainless steel hand K-Flexofile and rotary GT during the preparation of curved root canals in extracted human teeth. Methods:45 root canals of mandibular and maxillary molars with curvatures ranging between 25and 41 were divided into three groups.Based on radiographs taken prior to instrumentation with SS 10# K file inserted into the canal,the groups were balanced with respect to the angel and the radius of canal curvature,canals were prepared by Protaper or GT using a crown-down technique or by K-Flexofile using modified double flared technique.During the preparation, the canal were flushed with 2.5%NaOCL solution. At the end of preparation,each canal was irrigated with 10ml 2.5%NaOCL solution and 10ml 17% EDTA solution alternately,finally with 5ml distilled water.After splitting the roots longitudinally,two calibrated examiner(>0.9) quantified the amout of debris and smear layer on the basis of a numerical evaluation scale,using a scanning electron microscope .The data established for scoring the debris and the smear layer were separately recorded and analysed statistically using the Kruskal-Wallis test. Results: Completely clean root canals were never observed .On average, more effective cleaning was observed in the coronal and middle part of canals and significant difference were found between the coronal part and apical part(GT group and K-Flexofile group).For debris removal,Protaper achived better results than GT (P<0.05) and K-Flexofile (P>0.05); For smear layer removal,K-Flexofile achived better results than Protaper(P>0.05) and GT(P>0.05). Conclusion:Under the condition of this study,Protaper allowed significantly better removal of debris than GT and K-Flexofile,while K-Flexofile achived relatively better removal of smear layer than Protaper and GT.