Composite elastomers containing varying amounts of ammonium perchlorate (AP), hydroxyl terminated polybutadiene (HTPB) and toluene-di-isocyanate (TDI) with NCO/OH ratio unity were synthesised by γ-radiation over a dose range 0–720 kGy. To understand the polymer-filler interactions, stressstrain properties were determined after maintaining the samples at room temperature over 6 months. When progressively increasing either AP content or radiation dose the tensile stress increased and the strain decreased. The additional curing is attributed to the excessive crosslinking brought about by AP in the polymeric matrix.