With a binderless fluidized bed granulation method (Pressure Swing Granulation, PSG), jet-milled lactose particles were successfully agglomerated into narrow and spherical granules. This should be the first achievement of binderless granulation from an organic powder indicating the high potential of PSG application to pharmaceutical processes. With a decrease in the mean diameter of primary particles, the granules' mean diameter decreased, and the compression strength of a single granule increased. The size of product lactose granules predicted by the Iwadate-Horio [Powder Technol. 100 (1998) 223] model was in good agreement with the experimental results obtained by sieve analysis.