Provided are a method of selecting carriers and a device supporting the method. According to one embodiment of the present invention, a method for selecting carriers in a wireless communication system includes: receiving information on carriers and Channel Busy Ratio threshold from a network; selecting at least one carrier of which CBR value is below the CBR threshold; selecting a resource on the selected carrier; and transmitting a medium access control (MAC) packet data unit (PDU) by using the selected resource of the selected carrier.