Abstract: By using unidirectional cord reinforced rubber composites, the effect of generation heat on the fatigue behavior of rubber composites under cyclic loading was assessed. A great amount of heat was generated during the fatigue process of rubber composites. SEM photomicrographs show that the fracture surface of rubber composites under cyclic loading is closely interrelated with the generation heat. The energy loss which does not convert to effective heat generation is associated with fatigue damage in relation to the structural change leading to fatigue failure. It is found out that a quantitative relation exists between the average effective energy loss of fatigue damage and the fatigue life of rubber composites.