Thermal properties of mechanically alloyed aluminum particles filled DGEBA-MDA composite systems were investigated over a range of filler contents. Initial decomposition temperature increased up to a critical Al contents regardless of heating rate, beyond which the value depressed and then increased again with filler concentration of 40 phr. A TGA study of the composites showed that the presence of Al powder increases the thermal stability of the system through an increase in activation energy calculated by Toop's equation to a maximum at a critical filler concentration(20phr), beyond which the stability decreased slightly and increased again at 40 phr. The increase of thermal stability at 40phr is considered to be concerned with the formation of thermal conducting path dissipating thermal stress.