Background: Correct working length determination is an important step for successful endodontic therapy. Objective: The objective was to compare in vitro the accuracy of three electronic apex locators (EALs) (DentaPort ZX [Morita Co., Tokyo, Japan], SIROEndo Pocket [Sirona Dental Systems, NY, USA], and Rootor [Meta Biomed, Cheongwon-gun, Korea]) in detecting the major foramen using the clearing technique. Materials and Methods: Forty-five human extracted single-rooted teeth with mature apices were used for the study and divided into three groups of 15 teeth each. All teeth were embedded in an alginate model, and the electronic measurements were taken following the manufacturers orientations. Then, the teeth were cleared and photographed under a stereomicroscope with a digital camera. The distance from the file tip to the major foramen was measured using image analysis software program. Statistical analysis was performed using the Kruskal-Wallis, Mann-Whitney U, and Chi-square tests at a significance level of 0.05. Results: The mean distances from the file tip to the major foramen were 0.164 0.292, 0.162 0.234, 0.341 0.166 mm in the DentaPort ZX, SIROEndo Pocket, and Rootor groups, respectively. Statistical analysis showed that there was a significant difference between SIROEndo Pocket and Rootor (P < 0.05). However, no significant difference was found between DentaPort ZX and other EALs (P > 0.05). Conclusion: DentaPort ZX located the major foramen with 100% accuracy within the range of 0.5 mm. However, the accuracy of the SIROEndo Pocket and Rootor in locating the major foramen within 0.5 mm was 73.3% and 86.7%, respectively. All EALs showed an acceptable determination of the major foramen within the range of 0.5 mm.