Objective: This study aimed to evaluate and compare the mechanical behaviour of four brands of engine-driven NiTi endodontic instruments: HyFlex CM, made of controlled memory NiTi wire; Twisted File, made of R-phase NiTi; ProFile Vortex, manufactured from M-wire NiTi and RaCe, made of conventional NiTi. Materials and methods: Instruments were tested for bending resistance, cyclic fatigue, torsional resistance, Vickers hardness and toughness. Data obtained were statistically tested by analysis of variance and Student Newman-Keuls (SNK) multiple comparison tests. Results: The mechanical tests showed that instruments have different mechanical properties and performance. Conclusions: The results from this study showed that HyFlex CM files had the highest bending resistance, cyclic fatigue life and toughness. Keywords: cyclic fatigue, endodontic instruments, flexibility, nickel-titanium alloy, torsional resistance Conflict of interest statement: The authors deny any conflicts of interest related to this study.