We investigated the structural changes to normal and waxy rice starch samples caused by treating with a twin-screw extruder for the optimum utilization of rice powder by extrusion cooking. The moisture capacity and water-soluble carbohydrate levels of the extruded normal and waxy rice starch samples were markedly higher than those of the raw rice starches. The X-ray diffraction patterns of the raw rice starches were different from those of the extruded rice starches. No crystalline structure was apparent in the extruded rice starches. The λ _max and ε ₆₀₀ values with the iodine color reaction were unchanged in the all samples. However, gel permeation chromatography (GPC) performed with Toyopearl HW-75 showed only a single peak in the patterns for the extruded rice starch samples, indicating the presence of amylopectin decomposition products of low molecular weights. The intrinsic viscosity of the extruded rice starches was lower than that of the raw rice starches. These results indicate the value of extrusion cooking for rice powder with a variety of food processing methods.