Activated carbon (AC) was prepared from brewing yeast by Na2CO3 activation, and cobalt was supported on activated carbon (Co/AC) by the adsorption-activation method. The XPS test indicated that supported cobalt was Co(II). The total BET surface areas of prepared AC and Co/AC were 957.7 and 847.9m2/g, with total pore volumes of 0.81 and 0.80cm3/g, respectively. The average pore diameters of AC and Co/AC were found to be 3.8 and 3.3nm. The contact time required for equilibrium of methylene blue (MB) adsorption onto prepared AC and Co/AC was about 120min. The maximum uptake of MB by AC and Co/AC was estimated to be 372.1 and 213.5mg/g, respectively. The presence of prepared AC or Co/AC was advantageous for TOC reduction compared with UV/O3 system, and the greatest TOC removal was obtained in the presence of Co/AC. The kinetics of the degradation of MB fitted the Langmuir-first-order model well. The rate constants of Langmuir first-order were determined to be 0.0096min(-1) for UV/O3/AC and 0.0143min(-1) for UV/O-3/Co/AC, respectively.