The granulation of an organic powdered material in a tapered-fluidized bed has been studied experimentally and theoretically. The size and density of granules were measured under various conditions, and the effect of change in the fluidizing characteristics on these physical properties of granules were examined. As a result of this study, it was found that the factors dominating the physical properties of the granules were air velocity, the moisture content of the powdered material and the magnitude of the pressure fluctuation reflecting the size of the bubbles in the bed. From the theoretical consideration of the mechanism of granulation in the tapered bed, a granulation index consisting of these factors was newly proposed, and this index was found to be useful in expressing the physical properties of the granule in terms of a single factor.