Background: To compare the cyclic fatigue resistance (CFR) of Reciproc® Blue (RB), One Reci® (OR), R-Mo- tion® (RM), Roll Wave Gold (RW) and RCS Blue T (RCS B-T) instruments. Material and Methods: 525 files (105 RB (25/0.08), 105 OR (25/0.06), 105 RM (25/0.06), 105 Wave Roll (25/0.07) and 105 RCS Blue T (25/0.06) were assigned into 7 groups (n =15) for each brand. Group 0: Instruments were not exposed to NaOCl or sterilization. Groups 1 and 4: instruments were exposed to 5% NaOCl 1 and 3 times, respec- tively. Groups 2 and 5: instruments were sterilized 1 and 3 times, respectively. Groups 3 and 6: Instruments were exposed to both, NaOCl and sterilization 1 and 3 times, respectively. Subsequently, files underwent a dynamic CFR test. The chemical composition of the files’ surfaces from Group 0 was determined using energy-dispersive X-ray spectroscopy (EDS). Cyclic fatigue resistance time was statistically analysed using 1-way ANOVA and the Krus- kal-Wallis test. Post hoc multiple range analysis applying Tukey’s test and the Games-Howell test was conducted to assess significant differences. Results: Greater CFR values were observed in the RB instruments, followed by the RM, OR, RW and RCS B-T files, respectively (p˂0.05). No significant differences were observed among RM, OR and RW files (p˃0.05). The lowest CFR values were observed in the RCS B-T files(p˂0.05). The CFR of RB, RM, and OR decreased when the instruments were autoclaved and immersed in 5% NaOCl (p˃0.05) (3 times) compared with the control group. Conclusions: The RB displayed the best CFR values. The RB, RM and OR instruments were more vulnerable to the repeated cycles of NaOCl immersion combined with autoclave sterilisation. The high density of microstructural defects on the surface of RW and RCS B-T instruments, caused by a lack of quality control, makes their biomecha- nical behaviour unpredictable.