Some experiments were carried out on the mixing properties of medicinal powders and lactose granules of various particle sizes, using radionuclide indium-113m which has a short half life. ^113mIn was adsorbed by some medicinal powders such as lactose, crystalline lactose, Hustagin, Mino-Aleviatin, corn starch, and synthetic aluminum silicate. Lactose granules were prepared by the conventional method, using 10% starch paste as a binder, dried, and shifted into six particle sizes of 20-28, 28-35, 35-42, 42-65, 65-100, and 100-200 mesh. Mixing of medicinal powder and lactose was carried out with a YMQ-type dispensing mixer, three times for 5 seconds each. Mixing ratio was 1 : 2, 1 : 1, and 2 : 1 for medicinal powder to lactose granules. Experimental results indicated that the mixing properties were greatly affected by the physical properties of the medicinal powder, and this was especially marked in the case of Mino-Aleviatin and crystalline lactose, whose mixing became worse with increasing particle size of lactose granules. In a mixing ratio of 1 : 2, lactose, corn starch, and synthetic aluminum silicate showed good mixing with 100-200 and 28-35 mesh lactose granules. Mino-Aleviatin, Hustagin, and crystalline lactose showed poor mixing with lactose granules with particle size above 42-65 mesh. In 1 : 1 mixing ratio, lactose, Hustagin, corn starch, and synthetic aluminum silicate showed good mixing with lactose granules of all particle sizes. In 2 : 1 mixing ratio, synthetic aluminum silicate showed a poor mixing. It was concluded from these experiments that the fine granules used for dispensing should be of small particle size of less than 200μ (65 mesh).