The increased adoption of composite laminates in modern engineering requires advancement in the prediction of their dynamic behavior. Damping is a major design constraint in aerospace structures subjected to cyclic loads. While the effects caused by damping are well known, the mechanisms that cause it at the microscopic level are still unclear on a quantitative basis. Testing of these phenomena requires some difficulties to be overcome, like the contribution of spurious sources. The study focuses on the effects that the interphase has on the damping properties of carbon fiber-reinforced polymer (CFRP) composite structures. Three-phase models are employed to investigate the dependence of damping on the interphase mechanical properties, with a focus on the fiber-matrix interfacial shear strength. The experimental campaign confirms the attended results: in particular, a stronger interphase determines a lower damping of the structure.