Adhesion between fiber and matrix in fiber-reinforced polymer composites plays an important role both in controlling mechanical properties and in the overall performance of composites. This suggests that analytical and experimental methods to characterize the interface can be used to predict the mechanical performance of the material. To this end, vibration damping techniques have been used as a non-destructive method to evaluate interfacial effects on composites. According to the theory of energy dissipation, the quality of the interfacial adhesion can be evaluated upon separating the predicted internal energy dissipation associated with perfect adhesion from the measured internal energy dissipation of a composite system; this enables the quantification of interfacial adhesion. A micromechanics-based model for evaluating the adhesion between fiber and matrix from the damping characteristic of a cantilever beam was developed that shows an inverse relationship between the damping contributed by the interface and its adhesion strength. A simple optical system was used to measure the damping factor of unidirectional fiber-reinforced-polymer composites. Cantilever beam specimens containing either a single glass fiber or three types of single metallic wires embedded in an epoxy resin matrix were tested. A correlation was found between the measured interfacial adhesion strength directly from microbond pull-out tests and the micromechanics-based calculations from vibration damping experiments.