Anaerobic digestion is widely used as a traditional technology for sustainable biogas production from organic waste resources. Methane, carbon dioxide, and hydrogen are mainly included in biogas produced from organic waste. In order to improve utilizability of biogas as energy, it is necessary to improve methane content by reduction of carbon dioxide. Recently, trends of biogas upgrading researches have being altered from separation, reduction and recovery methods into direct methane conversion from carbon dioxide. In other words, carbon dioxide conversion into methane enhances biogas quality qualitatively and quantitatively. Electrochemical carbon dioxide conversion is promising technology for improving biogas quality efficiently and economically. Carbon dioxide can be converted into various hydrocarbon compounds such as methane directly on electrochemical Cu catalysts. Especially, methane selectivity mainly depends on catalyst materials and pretreatment methods. Therefore, in this study, effects of various pretreatment of Cu catalyst for maximizing methane selectivity on electrochemical conversion of carbon dioxide into methane were investigated. These results show that the physical and chemical pretreatments are more efficient than ultrasonical pretreatment. However, chemical pretreatment was not determined as more suitable method for improving selectivity than physical pretreatment because the non-reaction area by non-desorbed product on the rough surface of the electrode pretreated physically was not considered. Desorption of product by stirring can apply to improve selectivity of methane inaccurately analyzed by physical pre-treatment. Therefore, selectivity of physical treatment and chemical treatment was reanalyzed in consideration of the effect caused by stirring. As a result of the analysis, 25.14% of physical treatment and 23.62% of chemical treatment resulted in higher methane selectivity of physical treatment. Therefore, it is considered that the optimum method of preprocessing is a physical processing method, and additional measures are needed to reduce.