Effects of epoxy resin on various arylamine-based benzoxazine resins, i.e., aniline (BA-a), m-toluidine (BA-mt), and 3,5-xylidine (BA-35x), have been investigated. Processing windows of BA-35x, BA-mt, and BA-a were found to be widened with the amount of the epoxy. Gel points of benzoxazine-epoxy resin mixtures can be predicted by an Arrhenius equation, e.g., gel time of BA-35x and epoxy mixture at 70:30 mass ratio can be estimated by t(gel) = 0.7012 x 10(-7) exp (10.563/T). Glass transition temperature (T(g)) of BA-a and BA-mt alloyed with epoxy exhibited a synergistic behavior with the maximum T(g) value at the benzoxazine-epoxy composition of 80:20 mass ratio. However, in the BA-35x and epoxy mixture, the decreasing trend in T(g) from 241 degrees C to 223 degrees C with an addition of epoxy was observed. Furthermore, flexural strength and strain-at-break of those alloys were found to increase with increasing amount of the epoxy while modulus increased with the polybenzoxazine mass fraction. POLYM. ENG. SCI., 51:1797-1807, 2011. (C) 2011 Society of Plastics Engineers