INTRODUCTION: The aim of this study was to compare the sealing ability of Real Seal (RS) and Gutta-percha (GP). MATERIALS AND METHODS: Forty nine extracted human maxillary central incisors were used. The coronal part of each tooth was removed; the root canal was prepared using the crown down technique and apical enlargement to rotary file # 40. The specimens were randomly divided in to 3 groups of 15 each and two control groups of 2 each. Group 1, was obturated with RS and group 2 and 3 were obturated with GP and AH26 sealer by lateral condensation technique. In group 1 and 3 the smear layer was removed by 5mL of 5.25% NaOCl and 3mL of 17% EDTA. Leakage of the obturated roots was measured using the fluid filtration technique. This method was done at 2 min intervals for 8 min. data were analyzed using ANOVA and Tukey tests. RESULTS: Statistical analysis indicated significant differences between groups 2 with 1 and 3. The most leakage value was observed in the group 2. CONCLUSION: Root canal filling with RS or GP in combination with smear layer removal showed better sealing. Therefore the smear layer has more effect one apical leakage than the obturation system.