Objectives: The aim of this study is to evaluate the fracture resistance of pulpless teeth built up with resin composite with or without fiber post. Methods: Twenty four extracted human mandibular premolars were amputated at the cemento-enamel junction (CEJ). The post spaces (8 mm deep, 1.5 mm wide) were prepared using the exclusive post drills. The specimens were then divided into 3 groups according to the bonding area and post insertion: group 1 - both top of the root and post cavity was applied with Clearfil SE Bond, Fiber post (FibreKor) was inserted with DC core Automix, group 2 – dentin was treated as group 1, post space was filled with DC core Automix without post insertion, group 3 – only top of root was applied with Clearfil SE Bond, post space was filled without post insertion. Resin composite core (5 mm high) was built up with the same core material. After stored in water at 37 °C for 24 hours, the root of specimens were embedded in acrylic resin at 2 mm below CEJ. All specimens were loaded at 45 degrees to the long axis on a universal testing machine until fracture. The data (mean±SD (n=8), N) were analyzed by one-way ANOVA. Results: The fracture loads were, group 1: 1832.1±239.8 N, group 2: 1814.9±347.1 N, and group 3: 1810.4±332.4 N. There were no statistically significant differences among 3 groups. All specimens fractured in the composite resin core. Conclusion: Insertion of the fiber post did not affect the fracture resistance of pulpless teeth built up with resin composite. All groups showed restorable fracture mode.