Aim: The aim of this study is to measure the cyclic fatigue resistance of TruNatomy (Dentsply Sirona, Maillefer, Ballaigues, Switzerland) instruments in single and double curvature canals and compare it with those of ProTaper Next and 2Shape. Materials and methods: Sixty NiTi rotary files were used in this study and distributed into three groups (n = 20 for each group). Group I: TruNatomy (size 26, taper 0.04), group II: ProTaper Next (size 25, taper 0.06), and group III: 2Shape (size 25, taper 0.06). Then, each group was subdivided into two subgroups (n = 10 for each subgroup) according to the curvature of the canals (single or double). Lengths of all the used files were 25 mm. The files were tested in custom-made artificial canals with a single curvature (60° curvature, 5-mm radius) and a double curvature (coronal curve: 60° curvature, 5-mm radius and apical curve: 70° curvature and 2-mm radius). Each file was operated in a continuous rotation movement until the file fractures. Time for file separation and length of fractured fragment were recorded. The number of cycles to failure of each file was calculated. Statistical analysis: Data were statistically analyzed using the Shapiro-Wilk test, one-way ANOVA, and the post hoc Tukey test. Results: The normal distribution of data was detected by the use of the Shapiro-Wilk test. The results of the ANOVA test revealed a significant difference in cyclic fatigue resistant among three groups of the tested files (p < 0.05). The post hoc Tukey test showed that in both single- and double-curved canals, the number of cycles to failure of the TruNatomy group was significantly higher than other groups (p < 0.05). No statistical difference in fragment length among the tested files in both curvatures (p > 0.05). Conclusion: In both curvatures, TruNatomy instruments were more resistant to cyclic fatigue than 2Shape and ProTaper Next instruments.