The curing, compatibility, and fracture toughness of blends of 4,4’-bismaleimidodiphenylmethane (BDM)/tetraglycidyl diamino-diphenyl methane (TGDDM) were investigated. Diamino-diphenyl sulfone (DDS) was used as a curing agent. BDM alone could be both homopolymerized (at a lower temperature) and could also undergo Michael addition reactions with the primary amine of DDS. The secondary amine of DDS did not react with BDM. However, the network produced by homopolymerization was not miscible with that produced by the latter reactions. Curing of TGDDM with DDS took place almost at the same temperature as that of the homopolymerization of BDM, but well below the temperature of the Michael addition reaction. When a BDM/TGDDM mixture was cured with DDS In the stoichiometric ratio, the miscibility of the cured system increased with the amount of TGDDM. This was attributed to the fact that the network produced by Michael addition reactions was diminished. When DDS reacted entirely with TGDDM, the BDM/TGDDM/DDS cure yielded only a TGDDM/DDS network and a BDM homopolymerized network, which were not only miscible, but are also interpenetrating. The superior interpenetrated network, as indicated by the highest fracture toughness, was found at BDM/TGDDM = 40/60 weight ratio in the BDM/TGDDM/DDS curing systems.