Aluminum hydroxide aggregated particles which have an average particle diameter of not less than 40 .mu.m, an average particle diameter as determined after pressing at 1,000 kg/cm.sup.2 of not more than 35 .mu.m, and an L value of slurry obtained by mixing 20 ml of glycerol and 10 g of the aluminum hydroxide aggregated particles of not more than 69, are obtained by a process comprising the steps of: (a) feeding a supersaturated aqueous sodium aluminate solution to a vessel, (b) adding aluminum hydroxide seeds to the supersaturated aqueous sodium aluminate solution, (c) stirring the seed-added solution in the vessel while continuously feeding an additional supersaturated aqueous sodium aluminate solution into the vessel to hydrolyze the supersaturated aqueous sodium aluminate solution, (d) separating the aluminum hydroxide aggregated particles from the aqueous sodium aluminate solution, and (e) continuously discharging the aqueous sodium aluminate solution out of the vessel.