Mixing of powders and fine granules made by fluidized bed granulation that were different in particle size distribution was examined. It is prescribed in the Pharmacopoeia of Japan that more than 75 % of total fine granules pass through No.32 (500μ) sieve and remain on No.150 (105μ) seive, and not more than 10% of total fine granules pass through No.200 (74μ) sieve. Using lactose containing pigment as a raw material 2 sorts of fine granules, one having its peak at 42-65 meshes and the other at 65-100 meshes, were made with a fluidized bed granulator by modifying the granulating condition. Mixing epxeriment with the fine granules using lactose that is different in particle as a model of powder was performed. As a result, in case the mixture ratio was 1:1 the difference in mixing due to the difference in the particle diameter was scarcely observed. In case of the mixture with lactose of a fine particle size the granule having its peak at 65-100 meshes was the best of all in mixing, and in case of the mixture with lactose of a larger particle size the powders made by a fluidized bed granulation which indicated almost the same particle size distribution as the lactose showed the best mixing. In this way, it was found that the granules of a fine particle size were better in mixing with powder drugs on the conditions that they were without dispersiveness and adhesiveness.