The effects of molecular structures of ABS fabricated under a severe molding condition on rubber particle agglomeration and molded specular gloss were studied. An agglomeration index (N-p) Obtained by measuring particle size was used to determine the degree of rubber particle agglomeration. It was found that as graft level decreased, agglomeration increased. The rubber particle agglomeration also increased when graft molecular weight was increased. Lowering the particle size also led to a higher degree of agglomeration. Furthermore, increasing the compositional acrylonitrile mismatch between the grafted and matrix styrene-acrylonitrile copolymers increased the rubber particle agglomeration. Molecular structures that increased rubber particle agglomeration decreased the molded gloss.