Objectives: This study evaluated the influence of reciprocating movement on the fatigue life of root canal instruments subjected to static and dynamic tests. Materials and methods: The rotary NiTi instruments used in this study were WaveOne and ProTaper F2 (both from Dentsply Maillefer, Ballaigues, Switzerland). The instruments were initially subjected to a cantilever-bending test, then to static and dynamic fatigue tests. WaveOne instruments were operated in reciprocating movement and ProTaper in continuous rotation. Results: The mean bending resistance values (maximum load in grams) of the instruments were as follows: WaveOne = 544.8; ProTaper F2 = 555.4. No significant difference was observed between the instruments tested (P > 0.05). The mean time to fracture (in seconds) of the instruments subjected to static and dynamic tests were as follows: WaveOne = 93.5 (static) and 267.6 (dynamic); ProTaper F2 = 57.8 (static) and 94.1 (dynamic). Student's t test revealed significant differences in all tests (P 0.05). Conclusion: The findings revealed that instruments operated in a reciprocating movement and in the dynamic testing model presented prolonged fatigue life. Keywords: dynamic test, fatigue fracture, fatigue resistance, flexibility, reciprocating movement