In this study the thermal and mechanical behaviors of PP/mica composites, under dynamic conditions, are discussed on the basis of the changes induced by the presence of the interfacial modifier succinic anhydride-grafted atactic polypropylene, with different degrees of grafting, prepared in our laboratories by chemical modification of a by-product from industrial polymerization reactor. Changes in the interfacial activity, induced by the substitution of a very small amount of polymer matrix by the interfacial agent with different grafting levels, were conclusively obtained. The results obtained from either the thermal or the dynamic mechanical behavior led to the same conclusions, and agree with data obtained from macroscopic mechanical properties.