The characteristics of thermal degradation of epoxy system filled with natural zeolite were studied by thermogravimetry analysis (TGA). All the epoxy composites were degraded in one stage regardless of the zeolite content. In the Freeman & Carroll equation, the activation energy at 20 phr of zeolite was lower than that at any other content of zeolite and these values decreased with the increment of heating rate. In the Kissinger equation, activation energy decreased until 30 phr of zeolite was added and the value abruptly increased at 40 phr of zeolite content. The activation energy and thermal degradation temperature showed the same tendency according to the change of zeolite content. The activation energy obtained from the Freeman & Carroll equation was larger than that from the Kissinger equation.