This study compared the sealing ability of RoekoSeal, AH Plus and EndoRez in dog premolars after post-space preparation and exposure to the oral environment. Seventy-four root canals were cleaned, shaped and filled with gutta-percha and one of the sealers. Post spaces were prepared with about 4-mm root canal filling remaining in the apex. Teeth were sealed for 24 h for sealer setting. Teeth were exposed to the oral environment for 45 days. The dogs were killed and root canals were soaked in India ink and sealed for 96 h. The teeth were cleared, and leakage was measured under stereoscopy. The Kruskal-Wallis test was used for analysis. A significant difference was found between EndoRez and RoekoSeal groups (P < 0.05). EndoRez had lower leakage values than RoekoSeal after 45-day exposure to the oral environment. No statistic difference was found in the comparison of AH Plus with the other sealers under study.