Demand Response is a well-known means usually operated by the system operator(SO) or the electricity retailers in order to reduce the peak loads or cut the price in electricity market. KPX(Korea Power eXchange), the SO in Korea has been operating the demand bidding program(or the demand resource market) since it was firstly introduced as the pilot project in 2008. The results has proved to be effective to enhance demand response. This paper describes the basic concepts and the operation results of the program.