Background: The present study was conducted to evaluate influence of working length determined with three different electronic apex locators on the apical extrusion of debris using ProTaper Universal (PTU), ProTaper Next (PTN) and Wave One (WO) Ni Ti system. Materials & Methods: The present study was conducted among 60 extracted human permanent molars with mature apices. Electronic working length measurements were taken before and after preparation of the mesiobuccal canal with Root ZX, ProPex II and Endex apex locator using various irrigants. In group I, root canals were prepared with ProTaper Universal (PTU) to size F4/0.06, in group II with ProTaper Next (PTN) to size X4/0.06 and in group III with (Wave One) WO to size 40/0.08. Results: The mean difference in actual and final length was 0.191. Electronic length before preparation (EAL1) and after preparation (EAL2) was -0.21 in group I, in group II was -0.104 and in group III was -0.106. The mean difference in actual and final length was 0.194. Electronic length before preparation (EAL1) and after preparation (EAL2) was 0.208 in group I, in group II was -0.192 and in group III was 0.236. The mean difference in actual and final length was 0.198. Electronic length before preparation (EAL1) and after preparation (EAL2) was 0.201 in group I, in group II was -0.199 and in group III was 0.235. Conclusion: Authors found that the usage of apex locator to determine the WL decreased the amount of apically extruded debris. PTN caused less apical debris extrusion after determination WL with/without apex locator. Key words: Apex locator, ProTaper Universal, Working length.