Purpose: The aim of this study was to evaluate the bond strengths between various resin composites used as core materials (Multicore Flow, Ivoclar-Vivadent; Tetric Flow, Ivoclar-Vivadent; Filtek Flow, 3M-ESPE; Tetric Ceram, Ivoclar-Vivadent; Filtek Z250, 3M-ESPE), and an FRC post (FRC Postec Plus, Ivoclar-Vivadent) by means of the microtensile nontrimming technique. Materials and Methods: Five experimental groups were used. For the microtensile nontrimming technique, 45 to 50 beam-shaped specimens per group were obtained from cylinders of core material, which had been built up around the post by progressively adding small increments of composite resin. Each specimen was loaded in tension until failure at either one of the two post/core interfaces present in each stick. The differences in interfacial bond strength among the groups were tested for statistical significance with the one-way ANOVA test, followed by the Dunnett test for post-hoc comparisons. Results: The measured bond strengths in MPa were 17.29 ± 6.02 for FRC+MultiCore Flow, 16.37 ± 6.92 for FRC+Tetric Flow, 13.14 ± 5.35 for FRC + Filtek Flow, 12.38 ± 4.34 for FRC + Tetric Ceram, and 10.75 ± 5.43 for FRC + Filtek Z250. The statistical analysis revealed that MultiCore Flow achieved significantly higher bond strengths than Filtek Flow (p = 0.03), Tetric Ceram (p 0.001), and Filtek Z250 (p 0.001). The bond strength of Tetric Flow was significantly higher than that of Filtek Z250 (p = 0.003). Conclusion: For core buildup on a fiber post, dual-cure composites appear to be preferable to light-curing composites. Keywords: prefabricated FRC post, core material, composite resin, dual-cure composites, bond strength, microtensile testing