The aim of this work is to evaluate the thermal stability of the natural rubber- hard barium ferrite composites at a different content of ferrite particles. The tensile, hardness and swelling were tested before and after aging for 15, 30 and 45 days at 80oC. The composites were prepared by two roll mixing method. In this study, the composites vulcanizes were cured up to a respective cure time of each sample. Then aged for different periods for mechanical characterization. SEM images indicate no aggregation of the ferrite particles before and after mixing with rubber. Thermal stability of the composites during the first 2 weeks is noticed. After 15 days of aging, all the mechanical parameters decreased drastically with increasing aging time up to 30 days. The FTIR reflects the thermal stability of the composites. A Swelling test should the higher thermal stability and the optimum vulcanization parameter of the composites. For all samples, the thermal degradation increased after 15 days