PURPOSE: To prepare aluminum hydroxide with a low adhesive moisture capable of the economic treatment after the separation thereof, by adding a dehydration assistant to a slurry or washing water, and blowing steam on directly on aluminum hydroxide in separating the aluminum hydroxide from a mother liquor in combination.

CONSTITUTION: A dehydration assistant consisting essentially of a specific surfactant, e.g. a sulfosuccinate derivative, is added to a slurry of aluminum hydroxide before the separation or a washing water after the separation, and steam is then directly blown on the aluminum hydroxide to give the aimed aluminum hydroxide having about several % adhesive moisture. The amount of the dehydration assistant is about ≥10g/t Al2O3, preferably about ≥20g/t Al2O3, and the amount of th steam is about 5W6kg/t Al2O3, preferably about 10W 40kg/t Al2O3.In both cases, the dehydration assistant and steam need to be uniformly permeated into the aluminum hydroxide.