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 was prepared with Revo-S instruments. The cutting efficiency of 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 groups were instrumented according to the manufacturer’s recommendation, after preparation, each sample was re-weighted. The weight loss of each sample was being calculated. The data analysis showed statistically insignificant. Before preparation, each group of the files were subdivided into 3 groups, unused, after a 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 sign of deterioration.