A method and apparatus for handling of missing reference signal on unlicensed frequency in a wireless communication system is provided. The upper layer of the wireless device receives, from a lower layer of the wireless device, a first indication related to a first reference signal from a network, wherein the first indication is one of In-Sync (IS) indication or Out-of-Sync (OOS) indication. The upper layer of the wireless device starts a timer. The upper layer of the wireless device receives, from the lower layer of the wireless device, a second indication while the timer is running, wherein the second indication informs that a second reference signal from the network is missing. The upper layer of the wireless device increases a counter related to the first indication upon receiving the second indication.