Thermosetting terpolymer composed of benzoxazine (BOZ), cyanate ester (BADCy) and maleimide resin (BMI) was prepared via co-curing reactions. The curing reaction of benzoxazine with bismaleimide/ cyanate ester resin and the properties of the terpolymer were studied by differential scanning calorimetry (DSC) and Fourier transform-infrared spectroscopy (FT-IR), and the thermal, mechanical and dielectric properties of the terpolymer were also characterized. The FT-IR was applied to monitor the curing reactions of the reactive blends. Three reactions were observed in the curing reactions: the first is the polymerization of cyanate ester after oxazine ring opening, producing the triazine structure; the second is the coreaction between the triazine structure and benzoxazine, forming alkyl isocyanurate and diphenyl ether linkages, followed by the further reaction of the isocyanurate linkage; and the third is the self-polymerization of maleimide resin and benzoxazine, and coreaction with each other. Compared to the polybenzoxazine, the higher crosslinking density of the terpolymer led to the higher glass transition temperature (T-g), as well as the 5% weight loss temperatures (T-d5), indicating the better thermal stability of the terpolymer at service temperature. And the data for the mechanical and dielectric properties also showed that the terpolymer performs better than polybenzoxazine and the copolymer. (C) 2015 Elsevier Ltd. All rights reserved.