Abstract: The subject of the invention is a method for preparing fine-granuled starch from kernels of oats or rice. In the method, the kernels are ground and the starch is separated from the starch containing fraction obtained by the milling. An essential feature of the invention is that a suspension of the said fraction or of starch separated from it is treated with a surface-active agent or a lipolytic enzyme for disintegrating compound granules or aggregates of starch granules. Except the particle size, also functional properties of starch are affected. Disintegration of compound granules is enhanced by alkaline conditions and by mixing of the suspension. The fine-granuled starch obtained can be applied in foods and, for instance, for biodegradable plastics and for surface treatment agents. The invention can be included as a part of an integrated fractionation process, in which, in addition to starch, an oil fraction, an enriched fibre fraction, and a surplus fraction suitable for feed, are obtained.