We developed and evaluated an efficient method for the regeneration of activated carbon using dimethyl ether (DME), which is an organic compound that exists in gaseous state at room temperature and atmospheric pressures and liquefies above approximately 0.6 MPa at room temperatures. Liquefied DME dissolves both water and organic matter. When spent activated carbon adsorbs organic matter and water is immersed in liquefied DME, the organic matter and water are desorbed from the activated carbon and dissolved in the liquefied DME. Therefore, the spent activated carbon can be regenerated, and the activated carbon, organic matter, and water can be separated when the liquefied DME is depressurized. We developed and evaluated batch and flow methods for regenerating spent activated carbon polluted with acetic acid using DME. Using the batch method, the removal efficiency of the regenerated activated carbon for 1.0 wto/0 acetic acid solution was approximately 68%, whereas that of virgin activated carbon was 79%. The removal efficiency remained almost unchanged at 68% when activated carbon was repeatedly regenerated five times. We also conducted flow experiments to regenerate the spent activated carbon polluted with acetic acid. The removal efficiency of the regenerated activated carbon for 1.0 wt% acetic acid solution using the flow method improved with an increase in the contact time between the activated carbon and liquefied DME without being affected by the volume of the liquefied DME from 20 to 40 cm(3). The removal efficiency of the regenerated activated carbon was approximately 80%, an improvement of 18% compared to that obtained using the batch method, which almost corresponds to that of the virgin activated carbon obtained using the batch method. Additionally, the removal efficiency remained almost unchanged at approximately 80% when the regeneration process was repeated five times.