Adhesion at the fibre-matrix interface in fibre-reinforced composites plays an important role in controlling the mechanical properties and overall performance of composites. Among the many available tests applicable to the composite interfaces, the vibration damping technique has the advantages of being non-destructive as well as highly sensitive. An optical system was set up to measure the damping tangent delta of a cantilever beam, and the damping data in glass fibre-reinforced epoxy-resin composites were correlated with transverse tensile strength which are also a qualitative measurement of adhesion at the fibre-matrix interface. Four different composite systems containing three different glass fibre surface treatments were tested and compared. Our experimental results showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength.