The purpose of this investigation was to compare the ability of three Nickel Titanium (NiTi) rotary systems (ProFile, K3, and RaCe) to centralize instrumentation relative to the original canal location and to determine the distance of transportation of these canals. Sixty mesial root canals mandibular molars with curvature ranging from 15 to 40 degrees were selected. The canals were divided randomly into three groups of 20 canals each. The roots were sectioned horizontally at 3 mm, 5 mm, and 8 mm from the root apex. Teeth were reassembled and instrumented according to the manufacturer's guidelines, with all groups being prepared to size 30 (0.06) taper master apical file. The cross-sections were digitally scanned before and after preparation, and image analysis software was used to assess the centering ability and the extent and direction of transportation. The three groups were statistically compared with analysis of variance and Tukey's HSD test. The results indicated that all three rotary NiTi systems used in this study were able to preserve dentin structure. The RaCe system significantly showed most transportation (p<0.05). The ProFile system was found to be the best for all variables measured in this study.