Abstract: The activated carbon was prepared from walnut shell with H₃PO₄ by microwave irradiation. The effects of H₃PO₄ solution concentration, microwave power and activation time on the decolorizing capacity for methylene blue, iodine value and the yield of the activated carbon product was experimented. The best technology for preparing activated carbon with H₃PO₄ microwave irradiation was determined as: microwave power was 460 w, activation time was 10 min, H₃PO₄ solution concentration was 50%. The decolorizing capacity of the activated carbon manufactured under these conditions for methylene blue was 10.8 mL/0.1 g,the iodine value was 809.06 mg/g, and the yield of the product reached 52.96%. The activation time was as short as 1/9 of the traditional technology and the yield was 2.6 times of that by traditional technology.