A method and apparatus for transmitting a periodic reference signal in a wireless communication system is provided. An evolved NodeB (eNB) configures a periodic reference signal, and transmits the periodic reference signal in a specific duration. The periodic reference signal may be a discovery reference signal (DRS) or a channel state information reference signal (CSI RS). The periodic reference signal may be transmitted flexibly or transmitted by performing listen-before-talk (LBT) with reservation of transmission of the periodic reference signal.