The purpose of this study was to evaluate the efficacy of ProTaper Universal Retreatment files versus H-files in retreatment of canals obturated with Resilon and Gutta-Percha. Sixty extracted human single rooted teeth with straight root canals were selected. The canals were prepared in a crown-down technique using ProTaper Universal rotary instruments. The samples were divided into two equal groups of thirty samples each according to the obturating material used. Group I: Roots were obturated with Gutta-Percha and AH Plus sealer. Group II: Roots were obturated with Resilon and Epiphany SE sealer. Each group was further subdivided into two subgroups according to the technique used for retreatment. Subgroup A: Fifteen teeth from each group were retreated using H-files and chloroform solvent. Subgroup B: Fifteen teeth from each group were retreated using ProTaper Universal retreatment system. For each of the four subgroups, the canal wall cleanliness, the time required to reach the full working length was recorded and the time needed for satisfactory removal of the filling material was also recorded .The number of fractured instruments during retreatment was recorded. The retreated roots were grooved longitudinally and split into halves. Each half was photographed with a digital camera adapted to a stereomicroscope. The portions of the root canals that had the largest quantity of filling debris were selected for analysis. T-test and Parametric one-way analysis of variance (ANOVA) test were used to compare the percentage of the remaining filling materials after retreatment for each technique and the percentage of the remaining filling material in each third for the different groups. Two way analysis of variance (ANOVA) test was also used to examine the effect of the filling materials and that of the retreatment instruments. Gutta Perhca-H files recorded the highest mean value of the remaining filling material, followed by Resilon- H files and then Gutta Perhca- ProTaper while Resilon-ProTaper recorded the lowest mean value. Two way ANOVA revealed a non significant influence of the materials tested. It also revealed a non significant influence of the retreatment instruments. Regarding the total time taken for retreatment, Gutta Percha-H files recorded the highest mean value while Resilon-H files recorded the lowest mean value. Regarding the number of fractured instruments, when ProTaper was used, no instrument separation occurred. In conclusion, a completely clean root canal couldn't be achieved with any of the techniques investigated; Resilon was more readily removed from the canals than Gutta Percha. ProTaper performed better than H files.