Abstract: The effects of the ultrasound-assisted H₃PO₄ impregnation of sawdust on the pore structure, morphology, surface functional groups, and adsorption capacities for iodine and methylene blue of activated carbons produced from it were investigated. Results showed that ultrasonic impregnation promoted the mass transfer and uptake of H₃PO₄, which simultaneously increased specific surface area, pore volumes of micropores, mesopores and ultramicropores, and adsorption capacities for iodine and methylene blue. Long ultrasonic impregnation times were unnecessary. The maximum surface area (1 504 m²/g) was achieved at a total impregnation time of 45 min with 5 min ultrasound irradiation. Compared with impregnation without the ultrasound treatment, the ultrasonic-assisted impregnation reduced the impregnation time by 85%.