Disclosed in a method of discontinuous data reception in a mobile communication system. The method includes: receiving downlink data and decoding the received downlink data by the UE; when the decoding is not successful, starting a timer for receiving retransmitted data; when the downlink data has been received by a configured downlink assignment, operating a downlink carrier, through which the downlink data has been received, in an active time; and when the downlink data has been received by a dynamic transmission resource and the downlink carrier, through which the downlink data has been received, is different from a downlink carrier, through which a scheduling command for the downlink data has been received, operating the downlink carrier, through which the scheduling command for the downlink data has been received, and the downlink carrier, through which the downlink data has been received, in an active time.