The purpose of this study was to compare the shaping ability of two different NiTi rotary systems (ProFile GT Series X, and Protaper) in extracted human teeth using cone-beam computed tomography (CBCT) scanning. Methods:Thirty mesiobuccal canals of mandibular molars with angle of curvatures between 25°─ 45°degrees, were randomly divided into 2 experimental groups (n=15), according to the NiTi rotary system used, GT series X (GTX)and protaper groups. Canals were scanned before and after instrumentation by using CBCT scanner to evaluate root canal transportation and centering ratio at 3, 6, and 9 mm from the apex and volumetric changes. Data were statistically analyzed, and the significance level was set at P < .05. Results: GTX system showed significantly less canal transportation and more centering ability, compared to ProTaper system (P < 0.05).. GTX system, also showed significantly more dentine removal from the inner wall, at the level of 3mm, and less dentine removal from the inner wall, at the level of 9 mm from the apex, when compared to ProTaper system (P < 0.05). Conclusion:Within the limitation of this study, least canal transportation was produced by GTX system, with evenly dentin removal from canal walls. Furthermore, GTX instruments maintained the original canal curvature in curved canals, better than ProTaper instrument.