Abstract: Provided is a system for purifying biogas. The system for purifying biogas utilizes a separating unit for methane and carbon dioxide that connects to a separating unit for biogas and a separating unit for carbon dioxide to separate methane and carbon dioxide from the biogas. The separating unit for methane and carbon dioxide may separate the methane and the carbon dioxide. The separating unit for carbon dioxide may separate water and the carbon dioxide. The system for purifying biogas provides high concentration methane for use as fuel for motor vehicles and recycle the water to separate biogas repeatedly.