Amorphous high surface area aluminum hydroxide-bicarbonates were easily prepared by mixing an aqueous solution containing [epsilon-Al13O4(OH)(24)(H2O)(12)](7+) with an aqueous solution of sodium bicarbonate. The pH of the synthetic solution was controlled by the addition of aqueous sodium hydroxide, and amorphous composites with high surface area (>200 m(2) g(-1)) were obtained around pH = 7.5. The surface area decreased with the increase or decrease in pH (30 m(2) g(-1) at pH = 5.9 and 0.4 m(2) g(-1) at pH = 9.8). SEM and TEM images suggested that composites with high surface area were aggregates of nanoparticles.