The surface treatment of glass beads, chosen as model filler, with silane coupling agent with multilayer coverage was carried out. The treated beads were incorporated with poly(vinyl chloride), chosen as a typical ductile polymer. The effects of the organic functional group of silane and silane chain length on the mechanical properties of the filled composite were investigated. For this purpose, silanes having aminopropyl or methacryloxypropyl group as organic functional group with dialkoxy structure were used. The silane chain length on the bead surface varied from one to nine times the amount required for monolayer coverage. The yield stress was higher in the order of aminopropyl silane-treated > methacryloxypropyl silane-treated > untreated beads-filled systems. However, the elongation at break had a quite opposite order. The effect of silane chain length appeared only in the methacryloxypropyl silane-treated system. The yield stress increased slightly, whereas the elongation at break decreased with the increase of silane chain length. In the case of short silane length, the yield stress could be improved without decreasing of the elongation at break.