A bifunctional living poly(dimethylsiloxane), poly(DMS), was prepared through the anionic ring-opening polymerization of hexamethyl-cyclotrisiloxane (D3) with dilithium salt(2)of bis(p-hydroxydimethylsilyl)phenyl ether(1)as an initiator. The subsequent termination reaction with dimethylchlorosilane followed by the hydrosilation reaction of the end-standing silane function with allyl alcohol produced the uniform-size poly(DMS) with a hydroxypropyl group at both chain ends(4).The polyurethane/polysiloxane block copolymer having uniform-size poly(DMS) segments was then synthesized through the polyaddition reaction of the poly(DMS) having hydroxypropyl groups at both ends(4)with 4,4′-diphenylmethanediisocyanate followed by chain extension with 1,4-butanediol.