Objectives: The purpose of this in vitro study was to compare the sealing ability of two classes of endodontic sealers in overinstrumented root canal. Method: At first, 70 freshly extracted human maxillary anterior were selected. The anatomical crown were removed at the CEJ. The teeth were instrumented to a #50K MAF using the step back technique. During instrumentation the apical foramen was enlarged and kept patent to a#45K file. Then the teeth were divided into two tests (AH26 and Apexit groups)and two controls groups(negative and positive groups). Each test group has 30 teeth and each control group has 5 teeth. Root canals were filled with one of the sealers and gutta-percha using lateral condensation. After storage in 100% humidity at 37°c for one week, the root surfaces were coated with nail varnish ( exept at the apex), placed in 2%methilene blue dye solution and centrifuged. The roots were sectioned longitudinally to determine the following mean level of dye penetration. Results: Statistical analysis of the collected data showed that there was no significant differences between theAH26 group and Apexit group (p>0.05). Conclusion: AH26 and Apexit sealers seemed have the same sealing effect in overinstrumented teeth.