Background:The lateral canals are pathways for bacteria and their products to pass between the root canal and the periradicular tissue. Objectives: The present study aims to compare the filling ability of the lateral canals with three calcium silicate based sealers, including MTA Fillapex, Endoseal MTA and Sure-Seal Root, and AH26 epoxy resin sealer in the presence and absence of the smear layer. Materials and methods:Six lateral canals were prepared using an engine reamer in 80 single-rooted human teeth. The root canals were cleaned, then the teeth were randomly divided into two groups. In group A, the smearlayer was removed using 17% EDTA and 5.25% NaOCl, and in group B, the canals were irrigated with normal saline. Groups A and B were divided into four subgroups each, according to the sealer used: A1, B1 (MTA Fillapex sealer), A2, B2 (Endoseal MTA sealer), A3, B3 (Sure-Seal Root sealer), and A4, B4 (AH26 sealer). Obturation of canals was conducted by the warm vertical technique and then teeth were incubated for 72 hours. Teeth were made clear and the filling of lateral canals were evaluated under stereomicroscope. Results:In group A, the highest lateral canals filling rate was in subgroup A2 and the lowest in subgroup A1, and the difference was statistically significant. However, in both groups, the highest lateral canals filling rate was in subgroups B2 and B3 and the lowest in subgroup B1. However, the difference was not statistically significant. In addition, no significant difference was observed in the lateral canals filling rate considering their position in the root. Conclusion:Providing the removal of the smear layer, calcium silicate-based sealers, Endoseal MTA and Sure-Seal Root had a higher ability to fill the lateral canals than AH26 and MTA fillapex sealers.