Surface modified activated carbons(AC''''s) were prepared by HNO₃, and H₂O₂, treatment to enrich oxygen-containing functional groups on the surface of AC''''s. Acid treated AC''''s were applied to the separation of ammonia loom aqueous solution. Analytical techniques used to examine the physical properties include SEM and N₂ adsorption method and those used to examine the chemical properties include Electron Spectroscopy for Chemical Analysis(ESCA), CHNO analysis, slurry pH and IR. From ESCA analysis, phenolic, carboxyl and carboxylic groups occupied about 20 %, 1 % and 15 % of total functional groups, respectively. When AC''''s were treated with the solutions of 2 N and 10 N H₂O₂ and 1 N, 5 N and 10 N HNO₃, total oxygen contents were 2.47, 5.15, 9.62, 16.6, 19.1 % and BET surface areas were 1283.6, 941.8, 988, 840 and 560 m²/g, respectively. NH₃ adsorption isotherms of AC''''s were obtained at 30 ℃. For the AC''''s treated with the solutions of 2N and 10N H₂O₂ and 1 N, 5 N and 10N HNO₃ the amount of ammonia adsorbed from the 100ppm ammonia solution were 0.56,0.6, 0.65, 0.72,2.21 mg/g, respectively. The amount of NH₃ adsorbed on AC''''s increased with the total amount of oxygen-containing surface functional group. ion exchange ability with ammonium ion is thought to increase as the amount of carboxylic group(relatively strong acidic group) increases. No direct relationship between BET surface area of AC and NH₃ adsorption capability was observed.