In the framework of dispersive theory of strength, the effect of aggregation of initial disperse nanofiller particles on reinforcement degree is studied on the example of nanocomposites polypropylene/globular nanocarbon. It is shown that increase in aggregation degree of the indicated particles results to essential (approximately in order of magnitude) reduction of specific surface of nanofiller. The corresponding reduction is also observed for fractal dimension of nanofiller aggregates surface, which negatively affect on level of interfacial adhesion nanofiller—polymer matrix. Introduction of reduced filling degree within the framework of scaling model of reinforcement shown that this parameter can be used successively for correct determination of reinforcement degree of nanocomposites using micromechanical models. Thus, the reduced filling degree takes into consideration effects of nanofiller aggregation.