Background: The final stage of endodontic therapy is complete obturation of the root canal system to provide as perfect as possible at the cementodentinal junction of the apical foramen. The purpose of this in vitro study was to evaluate the sealing ability of injection molded thermoplasticized gutta percha and lateral condensation techniques with and without the use of sealers. Materials and Methods: Forty freshly extracted adult human maxillary central incisors with complete formed apices were utilized in this study. The teeth were randomly divided into four groups for evaluation of the apical seal. Group (1) lateral condensation gutta percha technique without sealer, (2) lateral condensation gutta percha technique with sealer, (3) Injection molded thermo plasticized gutta percha without sealer, (4) injection molded thermoplasticized gutta percha with sealer. Groups 1 through 4 were obturated as specified. All of the teeth were immersed in flourescine dye for 48 hours, then they were removed from the dye for microleakage measurement. Results: The results showed no significant differences between groups 1 and 3 and between groups 2 and 3 (p>0.05), but there were highly significant differences between groups 1 and 3 (p<0.01). Conclusion: Sealer was found to be an essential part of the thermo plasticized gutta percha and lateral condensation techniques. Thermo plasticized system with sealer had significantly less apical leakage than others. The highest amount of leakage was significantly seen with lateral condensation without sealer.