An agent is used to treat waste water containing dimethylsulfoxide and includes a solution of a porous material at a concentration of 6500 to 7500 mg/L, where an average size of pore openings of the porous material in a range of 60-550 m. The agent may be used in an aeration tank of a waste water treatment system, where the aeration tank is connected to a waste water tank for collecting waste water containing dimethylsulfoxide. A sedimentation tank of the system is connected to the aeration tank via a connection pipe for biologically decomposing the dimethylsulfoxide and settling sludge produced therein, and a treated water tank of the system returns a portion of treated waste water to the waste water tank and collects the remaining treated water therein.