Background: Accurate working length determination helps to decide the extent to which the instruments are placed. The present study was conducted to evaluate the effect of canal curvature on accuracy of apex locator. Materials & Methods: The present study was conducted on 54 mandibular molar teeth. The file clip of apex locator was attached to the file and the file inserted until the “Apex” reading was reached in Root ZX. This was the electronic working length (EWL). Differences between EWL and actual working length (AWL) were calculated. Results: Group I teeth were with root curvature < 20°, group II with 20-36° and group III with >36°. Each group had 17 teeth. Maximum difference was observed in group III, followed by group II and group I. Conclusion: Authors found that mild curvature group revealed better reading with apex locator than moderate and severe groups.