Poly(benzoxazine-co-urethane) was prepared by melt-blending bisphenol-S/aniline-type benzoxazine (BS-a) with isocyanate-terminated polyurethane (PU) prepolymer based on 2,4-toluene diisocyanate and poly(ethylene glycol), followed by thermally activated polymerization of the blend. The copolymerization reaction between BS-a and PU prepolymer was monitored using Fourier transform infrared spectroscopy. The morphology, dynamic mechanical properties, and thermal stability of the poly(benzoxazine-co-urethane) were studied using scanning electron microscopy, dynamic mechanical analysis, and thermogravimetry. Homogeneous morphology is shown in scanning electron micrographs of the fracture surfaces of poly(benzoxazine-co-urethane)s with different urethane weight fractions, and the roughness of the surface increases with urethane content increasing. Correspondingly, a single glass transition temperature (T-g) is shown on the dynamic mechanical analysis curves of the poly(benzoxazine-co-urethane)s, and the T-g is higher than that of the polybenzoxazine. With increase in the urethane content, the T-g and water absorption of poly(benzoxazine-co-urethane) increase, whereas the storage modulus and thermal stability decrease. (c) 2013 Society of Plastics Engineers