aim: to study canal transportation and centric ability of four different NiTi rotary systems in curved canals.   materials  and methods:  forty extracted mandibular first molars with similar length and root curvature were selected. All teeth were accessed and working length determined. Teeth were embedded in heavy body rubber base impression material after cutting of distal root to the cervical level. The teeth were randomly assigned to four groups, ten for each. Group I was prepared with ProTaper universal up to F2, group II was prepared with ProTaper Next up to X2, group III was prepared with WaveOne up to primary file,  and group IV was prepared with Wave One Gold up to primary file. All teeth were submitted to Pre and post instrumentation scanning with multislice CT and root cross-sections were saved and compared at three levels; 3 mm from the apex (apical), 3mm from the canal orifice (coronal), and mid way between the two measurements (middle). Canal transportation and centric ability were estimated and statistically analyzed.   Results: there was no significant difference between the four groups in apical and coronal levels, but, in middle part, there was a significant difference between them regarding canal transportation and centric ability.   Conclusion: the WaveOne Gold NiTi primary reciprocating file maintained the original canal anatomy with less modification of the canal curvature compared with other file systems up to apical size 25.