To overcome the brittleness of polybenzoxazine and decrease its high curing temperature, sulfonated polysulfone/polysulfone/benzoxazine ternary blends were prepared, and their curing behaviors, phase structures and properties were probed. Sulfonated polysulfone (SPSU) was synthesized firstly, and then SPSU was applied to modify 4,4′-diaminodiphenyl methane based benzoxazine (BZ-m) along with polysulfone. The results obtained from differential scanning calorimetry showed that the addition of SPSU efficiently decreased the curing temperature of BZ-m, and furthermore affected the phase structures of SPSU/PSU/PBZ-m blends. The phase structures of the corresponding blends were confirmed by scanning electron microscopy and dynamic mechanical analysis to probe the relationship between the microstructures and mechanical properties. According to the results, the blends presented complicated phase structures and exhibited good comprehensive mechanical properties. Moreover, all the blends displayed good thermal stability and the blends with SPSU-PBZ-m core − shell particles and a phase inversion structure exhibited the highest comprehensive mechanical properties. We believe these blends can meet the requirement of applications relating to high strength and good toughness matrix for fiber reinforced composites. © 2014 Society of Chemical Industry