This paper presents an in-depth review for current status for demand-side management (DSM) investment of energy supplier and an useful prospect on the introduction of Energy Efficiency Resource Standards (EERS). According to the Article 9 of Rational Energy Utilization Act, Energy suppliers-Korea Electric Power Corporation (KEPCO), Korea Gas Corporation (KOGAS) and Korea District Heat Corporation (KDHC) prescribed by Presidential Decree-must establish and implement annual demand-side management investment plan to improve energy efficiency in production, transformation, transportation, storage and usage of corresponding energy and to reduce demand and green house gas emissions. In this paper, we examine the DSM programs of energy suppliers and the results of DSM investment in 2009, then we propose a reasonable solution for the development of DSM investment. Furthermore, in order to compare our situation, the case studies were conducted on EERS issues in England, Italy, France and U.S, such as establishing the energy saving target, selecting the target energy supplier, and penalty and incentive mechanisms. Throughout the case studies, this paper suggests the directions to the DSM investment planning of energy suppliers and the major issues to prepare EERS in Korea.