An inorganic filler, natural zeolite was incorporated into ABS in this study. We observed the effect of natural zeolite on rheological properties and thermal properties of ABS/Zeolite composites. The melting viscosity was increased with increasing zeolite content at a constant shear rate but it was independent of paritecle size. At a constant temperature, entrance correction, e was expressed by equation of Y=aln(x) + b. The siope $alpha$ was 055~0.56 regardless of zeolite content. The flow activation energy varied with shear rates. Thermal stability investigated by TGA depended on the zeolite content. As zeolite content increased, $T_{d}$(thermal decomposition temperature) and activation energy of thermal degradation increased. Therefore, addition of zeolite contributed to the thermal stability of ABS/Zeolite composites.