The influence of coupling agent (Si69) on heat build-up (HBU) and the resistance to blowout temperature was investigated on vulcanised natural rubber (NR) containing 50 p.p.h.r of precipitated silica. The amount of Si69 was varied from 1 to 6 parts from hundred of rubber (p.p.h.r.). The HBU increased as the amount of Si69 was increased. The increase in HBU was consistent with increase in hysteresis as the amount of Si69 was increased. Increase in hysteresis with increasing Si69 might be attributed to the breaking of rubber- filler interaction via coupling agent as reflected by the Youngs modulus measurement. Youngs modulus decreased progressively as the applied static loading was increased which might be associated with breaking of the rubber-filler interaction. Concomitantly, the volume fraction of rubber (Vr) in the swollen gel also decreased with increasing applied static loading. The Vr, in swollen gel increased as the amount of Si69 was increased for both cases before and after subjection to cyclic loading at 10 MPa for 10 cycles, thus indicating the enhancement of rubber-filler interaction with increasing Si69. The blowout temperature measured in the interior of the test piece was about a factor of 2 higher than that recorded at the base of the test piece. The blowout temperature increased as the amount of Si69 was increased due to enhancement of the rubber-filler interactionvia coupling agent Si69 as indicated by the increase in Vr with increasing Si69 both before and afterblowout failure.