An evaluation of the fibre/matrix interfacial shear strength was performed by the single-fibre fragmentation tests on polypropylene-glass fibre microcomposites filled with various types and amounts of silica nanoparticles. In particular, both non-functionalized and dimethyldichlorosilane-functionalized silica nanoparticles were added up to a weigth content of 7%. Moreover, the effect of various amounts of maleic anhydride modified polypropylene (PPgMA) on the fibre/matrix adhesion was also investigated, including some selected formulations containing both PPgMA and silica nanoparticles. Interfacial shear strength was found to remarkably increase (up to a factor of about 5 for a 7 wt% content of surface treated nanoparticles) with respect to the case of neat polypropylene matrix. The observed effect was explained by considering that silica nanoparticles increase the work of adhesion of polypropylene with respect to glass, as proven by contact angle measurements in different liquids. In addition, silica nanoparticles promoted a remarkable enhancement of both elastic modulus and creep stability of the selected polypropylene matrix.