The diglycidyl ether of bisphenol-A epoxy resin (EPON 828(R)) was cured with 4,4＇-diaminodiphenylsulfone (DDS) and, optionally, an animophenyl functional reactive polyethersulfone (R-PES, = 10k) as a co-curing agent. Commercial polysulfone, Udel(R) P-1700, was also utilized to afford epoxy-Udel(R) blends (or semi-IPNs). Cured epoxy polymers were subjected to T-g determinations, plane strain fracture toughness (K-IC) tests, adhesive bond strength measurements, tensile tests and chemical resistance studies. The morphologies of the fractured samples were studied by SEM and correlated to the property changes. Only the reactive polysulfone modification improved both fracture toughness and adhesive properties without detracting from the good mechanical properties and chemical resistance.