Processing technology was studied basically for microcellular plastics in this paper. The continuous processing system was constructed using extruder and was verified propriety of this system. In order to investigate cell morphology and cell structure, microcellular polystyrene samples were produced under various conditions by the above processing system. Concretely, foaming die which can be varied pressure in die was prepared. The effect of pressure drop in die on cell morphology of microcellular plastics was examined using this changeable die. In addition, the effect of blowing agent contents, temperature in die and besides additioner on that of microcellular plastics were also investigated.