Moisture-cured polyurethane is one of the commercially important polymers, which is widely used in sealants, coatings, and reactive hot-melt adhesives. A series of moisture-cured polyurethane/polysiloxane (PUSR) copolymers were successfully prepared using a two-step solution polymerization procedure. Both amine-terminated polysiloxane (PDMS) and polyester diol were together used as mixed soft segments to react with 4,4'-diphenlymethane diisocyanate (MDI), and the alkoxysilane was used as end-capping agents. The effects of structure variation of building blocks such as the polyester diol structure and NCO/OH ratio on the properties and morphology of PUSR copolymers were studied. The tensile properties, dielectric behavior, thermal stability, surface, and water-repellency properties were investigated. The results showed that the properties and morphology of PUSR copolymers were greatly affected by the variations in molecular architecture. (C) 2008 Wiley Periodicals, Inc.