This study was designed to evaluate the cutting efficiency and defects influencing surface topography of HeroShaper and Revo-S NiTi rotary files.90mesiobuccal root canals of extracted permanent mandibular first molar, with fully developed apices and curvature ranging between 25-35 degree. Samples were divided into two groups according to the instrument used for canal preparation where, group A prepared with HeroShaper and group B prepared with Revo-S instruments. The cutting efficiency of the both tested systems was evaluated by randomly selecting 10 samples from each group. The selected samples were weighted by a highly sensitive 5 digits scale, then each sample in both group were instrumented according to the manufacturer recommendation, after preparation, each sample was reweighted. The weight loss of each sample was being calculated. By the data analysis showed there is no statistically significant. Before preparation each group of the files were subdivided into 3 groups, unused, after single use and after 9 uses. Both files showed no visible defect, and with SEM there was no statistically significant difference in unused and after single use, while the Revo-S rotary instrument demonstrated the incidence of fracture after 9 uses. It could be concluded that the rotary Ni-Ti instruments should be examined prior to instrumentation using any type of magnification to check if there is a signs of deterioration.