Aim: This study aimed to compare the fatigue behavior of resin composite and dental amalgam restorative materials used below the occlusal rest of removable partial denture (RPD). Subjects and methods: Thirty extracted first maxillary molars were prepared with standard class II cavities and divided to three groups (n=10 per group). Group I and group II were filled with composite (Charisma Smart and Flitek Z250) respectively and group III was filled with amalgam (Dispersalloy). After 24 hours, 30 standard saucer shaped rest seats were prepared. The samples were stored in distilled water for 14 days prior to testing. Fatigue resistance test was evaluated by the step-test method on a computer controlled materials testing machine. One way ANOVA followed by pair-wise Tukey's post-hoc tests was used to determine the significance between groups. Results: The difference between groups was statistically non-significant as indicated by the one way ANOVA followed by pair-wise Tukey's post-hoc multiple comparison tests (p=8910>0.05). Conclusion: There was insignificant difference in the fatigue fracture resistances between the tested groups.