A landfill leachate treatment plant (LLTP) in Korea was retrofitted to improve treatment efficiency by using integrated membrane process that is composed of membrane bioreactor (MBR) and reverse osmosis (RO) process. In general, proper treatment of landfill leachate is difficult for its refractory contaminants and widely variant volume due to irregular rainfall. Therefore various advanced physicochemical treatment processes have been developed. These processes are mainly composed of biological and physicochemical processes and they are very effective and economical in the early stage of landfill. But as landfill ages, the characteristics of landfill leachate changes to have lower biodegradable organic matters and highly concentrated nitrogenous compounds. In this case biological oxidation of organic compounds and denitrification of nitrogenous compounds hardly functioned. To solve these problems, we used the integrated membrane process and adopted both MBR to enhance the removal efficiency of biodegradable organic matters and nitrification rate and RO to remove physically the remaining inorganic nitrogenous ions and non-biodegradable matters. As the result, the effluent water quality met the enhanced regulation limits and continual public complaint was resolved.