By using reactive polydimethylsiloxanes that have phenolic hydroxyl groups at the ends of the chain, a polycarbonate-polydimethylsiloxane (PC-PDMS) block copolymer was prepared, and the properties of fibrous glass reinforced plastics (GF-PC) using this copolymer were examined. The Izod impact value of the PC-PDMS/GF composite increases with an increase in the degree of polymerization of reactive PDMS (n) between 40 and 160. When n is 40, the Izod impact value of the PC-PDMS/GF composite is equal to that of the PC/GF composite. The Izod impact value is independent of the PDMS content of the copolymer when it is between 2 and 4 wt %. The PC-PDMS/GF composite is superior, in the balance between fluidity and impact resistance, to the PC/GF composite. From the results of SEM, adhesion between the polymer and GF of the PC-PDMS/GF composite is superior to that of the PC/GF composite.