Statement of problem: Retreatment procedures in endodontics requires the complete removal of the original root filling materials. The most common materials that must be removed during retreatment are gutta-percha and sealers.Purpose: The aim of this in vitro-experimental study was to compare the amount of residual filling material after retreatment of the root canal walls which were obturated with gutta-percha or Resilon.Materials and Methods: Thirty extracted premolar single root human adult teeth were selected and prepared by race rotary files up to MAF#35. Then, they were divided into two groups of 15 (A and B). Group A was obturated with gutta-percha and AH26 sealer and group B with Resilon system by lateral condensation technique.  After 4 weeks all the canals were retreated by Race rotary files and the use of chloroform and master apical file increased to #40 file. Then, the teeth were split longitudinally and the remaining materials on the surface of the canals were visualized with streomicroscope with 20 magnification and digital photographs captured. The amount of residual materials and time of retreatment were analyzed with Mann-Whitney and Freidman tests.Results: The highest residual material value was in Resilon group and the difference between the two groups was significant (p <0.001). The time required for retreatment was not significant between the two groups ( p =0.381)Conclusion: Orthograde retreatment of Resilon was less efficient than gutta- percha with more residual materials on the surfaces of the root canals that were filled with Resilon.Key words: Retreatment, Resilon/ Epiphany system, Rotary instruments