Aim: To compare the cross-sectional area of sealer plus voids of gutta-percha/AH Plus and Resilon/ RealSeal following root canal preparation with rotary nickel-titanium ProTaper instruments and different apical preparation sizes. Materials and Methods: Forty-eight extracted maxillary anterior teeth were instrumented with the ProTaper system to apical sizes of 25 (F2), 40 (F4) and 60 (F5 + K-files) (n = 16 each). The teeth were divided into six groups (n = 8) for obturation as follows: group 1, apical preparation size 0.25 mm + gutta-percha/AH Plus sealer; group 2, apical preparation size 0.25 mm + Resilon/ RealSeal; group 3, apical preparation size 0.40 mm + gutta-percha/AH Plus sealer; group 4, apical preparation size 0.40 mm + Resilon/RealSeal; group 5, apical preparation size 0.60 mm + guttapercha/ AH Plus; group 6, apical preparation size 0.60 mm + Resilon/RealSeal. All root canals were filled using the warm vertical compaction technique. Horizontal sections were obtained every 1 mm, up to 3 mm from the apical foramen. Samples were observed by scanning electron microscopy under x200 magnification. Sections were digitally photographed under a stereomicroscope and the images were transferred to a compatible PC for image analysis. Using a computer program, the surface areas of voids were calculated and compared statistically for different preparation sizes and obturation systems at all levels, using the Kruskal-Wallis test with Sidak correction and Mann- Whitney U test (P 0.05). Results: Comparisons within each obturation group (gutta-percha/AH Plus and Resilon/RealSeal) showed the presence of voids, but there were no significant differences between the two groups for apical preparation sizes of 25 and 40 (P 0.05), irrespective of the level of sectioning. The only significant difference was obtained for canals prepared to an apical size 60: canals obturated with Resilon/RealSeal showed significantly more voids than those filled with gutta-percha/AH Plus, especially at the 3-mm level. Conclusions: Resilon/RealSeal did not achieve better results in terms of sealing ability in the apical third when compared to the conventional obturation materials gutta-percha/AH Plus. Keywords: AH Plus, gutta-percha, RealSeal, Resilon, sealer area