The aim of the present study was to evaluate and compare the shaping abilities of nickel titanium Reciprocating Single-file instruments (Reciproc) and (WaveOne) versus Full-sequence Rotary instruments (Twisted File) when used in preparing curved root canals regarding the following criteria: Change in canal curvature (degree of canal straightening), Degree and direction of canal transportation, Canal centering ability and Volume of removed dentine, using Cone Beam Computed Tomography (CBCT). Materials and methods: Forty five extracted human permanent mandibular first and second molars with the curvature of the mesiobuccal root canals ranging between 20-40 degrees were selected, standard endodontic coronal access cavities were prepared, Mesiobuccal canal orifices were located, Working length of all samples was standardized at 17 mm by flattening the teeth crowns. Teeth are placed in transparent acrylic resin block still CEJ. The teeth were divided into three groups with 15 teeth each: group A (Reciproc), group B (WaveOne) and group C (Twisted File). The samples were arranged in a specially fabricated cartoon box, then the teeth were scanned using CBCT. Mesiobuccal root canals were instrumented with different systems. Using pre- and post-instrumentation radiographic scanning and measurments, degree of canal straightening, volume of removed dentine were calculated, degree and direction of canal transportation and centering ratio were calculated at each pre-determined level (apical, middle, coronal) in mesial, distal, buccal and lingual directions, according to Gambill method, Statistical analysis of data was performed, the significance level was set at P ≤ 0.05.Results: All the three systems showed a significant straightening in canal curvature with no significant difference among the three systems. No significant difference among the three systems in degree of canal transportation and centering ratio at all levels of root canal in both mesiodistal and buccolingual directions except at cronal level in mesiodistal direction, RC and WO showed significantly higher canal transportation than TF, and TF showed significantly higher centering ratio than RC and WO. RC and WO showed buccal transportation significantly higher than TF at apical and cronal levels. No significant difference among the three systems in volume of removed dentine.Conclusions: The single file reciprocating systems (RC and WO)and full-sequence rotary system (TF) were capable of shaping of curved canals with a relatively good shaping ability in terms of maintaining original canal curvature, canal transportation, centering ability and volume of removed dentine. Reciproc, WaveOne and Twisted File caused significant straightening of root canal curvatures. All the three systems were able to remain centered within the canals with a degree of transportation. The three systems significantly decreased the root volume.