Background/purpose: The aim of this study was to evaluate the effect of different fiber-reinforced composites (FRCs) on the shear bond strength of composites bonded to tooth structures. Materials and methods: One hundred human non-carious upper central incisors were used. The FRC test specimens consisted of 4 commercially available polyethylene fiber products (Ribbond, Construct (CT), glass-fiber everStick (ES), and Stick, and one nanohybrid composite (Grandio), bonded to the vestibular surface of adhesive-treated enamel and dentin. Control groups were prepared using the nanohybrid composite along without fiber reinforcement. Specimens were stored wet for 24 hours at 37°C and thermocycled 5000 times between 5 and 55°C. Then, the shear bond strength (SBS) was determined using a universal test machine (Instron) at a crosshead speed of 0.5 mm/min. The failure patterns of the debonded specimens were evaluated using a stereoelectron microscope. Scanning electron microscopy (SEM) was used to assess the fiber resin interface of representative samples. SBS data were analyzed using analysis of variance (ANOVA) and Duncan’s test (α = 0.05). Results: SBS data ranged 21.54–40.18 MPa for the enamel substrates and 20.83–36.87 MPa for the dentin substrates. The one-way ANOVA results revealed statistically significant differences between the shear bond strengths of the experimental and control groups (P < 0.001). Two-way ANOVA of the experimental groups demonstrated statistically significant differences in SBSs between different fiber types and substrates (P < 0.05). A typical SEM micrograph of the surface of the fractured specimens following the shear bond test exhibited no evidence of debonding between the fiber and matrix when using the CT and ES fibers. The SEM analysis revealed that Stick fiber reinforcement contained some air voids in the final FRC structure. Combined cohesive and mixed fracture modes at the tooth/composite interface for CT/enamel, CT/dentin, ES/enamel, and ES/dentin were 50%, 60%, 40%, and 30%, respectively. The adhesive fracture mode was predominant in the control groups. Conclusions: The addition of an FRC at the interface showed positive effects on the SBSs of the composite bonded to the tooth structure and resulted in changes in the fracture pattern.