Background: Root canal obturation is an important step in endodontic treatment, which is performed aiming to three-dimensionally seal the canal and prevent microleakage, reentry, and proliferation of microorganisms in the root canal system. On the other hand, microleakage eventually leads to root canal treatment failure. Sealing ability is an important property of endodontic sealers. This in vitro study aimed to compare the quality of apical seals obtained by three endodontic sealers. Materials and Methods: This in vitro experimental study evaluated 48 extracted single-canal maxillary incisors. Hard- and soft-tissue residues were removed and the teeth were immersed in 5.25% of sodium hypochlorite for disinfection. The teeth were decoronated at the cementoenamel junction with a diamond disc such that 10 mm of root length remained. Canal patency was ensured using a #10 K-file. The canals were then instrumented with ProTaper rotary system. The canals were randomly divided into three experimental groups for the application of Adseal, Proseal, and AH26 sealers, and positive and negative control groups. Sealers were applied in the canals using lateral compaction technique. The external root surfaces were then coated with two layers of nail varnish except for the apical 3 mm. The amount of microleakage was quantified using the dye-penetration technique. The Tukey's test was used to compare the microleakage between the experimental and control groups. The Kruskal-Wallis test was applied to compare the microleakage of experimental groups (P < 0.05). Results: The amount of microleakage in canals filled with Adseal, Proseal, and AH26 sealers with lateral compaction technique was 2.33 ± 0.64, 2.2 ± 0.81, and 2.22 ± 0.71 µm, respectively. No significant difference was noted among the three sealers regarding microleakage (P = 0.84). However, the amount of microleakage in the sealer groups was significantly lower than that in the control group (P < 0.001). Conclusion: The application of Adseal, Proseal, and AH26 had equal efficacy for the provision of optimal apical seal in filling of root canals with lateral compaction technique. The application of sealers yielded a significantly superior apical seal compared with the control group.