Three-dimensional shape analysis of rice grains was examined with an automatic image processing system. Each 50 grains of polished and unpolished rice of the same kind were analyzed with both a manual method by a dial-gauge and the automatic image processing system. As a result, it was observed that there was little significant difference between the values (length, width and thickness) obtaimed by two methods. Furthermore, it was suggested that this system is more useful for quick calculation of the true polishing ratio as compared with the manual method. From these results, it is concluded that the automatic image processing system is expected to be suitable for the control of rice polishing process.