Modified DGEBA epoxy resin system was prepared using epoxy phenolic novolac (EPN), bisphenol A cyanate ester prepolymer and polyether sulphone (PES). DGEBA epoxy resin modified with cyanate ester prepolymer offers process advantage in making prepregs for the preparation of structural composite materials. Further, the DGEBA epoxy resin modified with EPN and PES along with cyanate ester prepolymer was fully polymerised by curing at 200degreesC for 4 h. The cured resin was characterised by FT-IR, thermogravimetric analysis and differential scanning calorimetric methods. The moisture resistance properties were studied for the cured resins. The morphology studies were done for cyanate ester monomer, cyanate ester-epoxy polymer and PES-modified cyanate ester-epoxy polymers. Carbon fibre laminates were made based on PES-modified cyanate ester and epoxy polymer. Mechanical properties of the laminates were evaluated.