We report a simple and mass-producible method for incorporating multiwalled carbon nanotubes (MWCNTs) on the surface of chopped glass fibers for applications to glass-fiber reinforced plastics. The MWCNTs were synthesized by thermal CVD. In order to eliminate impurities in the MWCNTs (such as metallic catalysts), the MWCNTs were treated in acid mixture (sulfuric acid/nitric acid=3:1 (v/v)) at $70^{circ}C$ for 24 h, followed by a reflux process in 5 M HCl at $120^{circ}C$ for 6 h. The multiple fillers, such as MWCNTs/glass fibers for reinforcement, were prepared by dipping the chopped glass fibers in a well-dispersed alcohol MWCNT solution (0.1 wt%). Field emission scanning electron microscopy showed MWCNTs generated on the microscopic glass fibers. Moreover, the MWCNTs piled up on the surface of the glass fibers with increasing absorption time. The mechanical properties of the ABS were enhanced by the incorporation of MWCNT-coated glass fibers.