To provide a method for producing -(1,3)(1,6) glucan from gulcan-containing celluar source, treatment composition containing gulcan and the use/method of the treatment.

This method comprises the following process: (a) the cells containing gulcan are extracted with alkali under heating to remove alkali soluble components; (b) the cells of the step (a) are extracted with acid under heating to prepare suspension; (c) the suspension obtained in the step (b) or collected and hydrolyzed cells are extracted with an organic solvent having a density larger than that of water, to separate into the water layer containing -(1,3)(1,6)-glucan particles and the organic layer and remain only the water layer substantially containing -(1,3)(1,6) glucan particles. The extraction with the organic solvent can separate branched -(1,3)(1,6) glucan from substantially unblanched -(1,3) gulcan associated with residual non-glucan contaminants; and (d) the glucan substance from (c) is dried, to give the fine gulcan particles.