A method and a base station for transmitting downlink data to a user equipment configured with a plurality of serving cells; and a method and a user equipment configured with a plurality of serving cells for receiving downlink data are discussed. The method for transmitting downlink data according to an embodiment includes transmitting a physical downlink control channel (PDCCH) carrying a downlink grant through a scheduling cell; and transmitting a physical downlink shared channel (PDSCH) carrying the downlink data through a scheduled cell. A primary cell (PCell) group is configured with a PCell and zero or more secondary cells (SCells), and an SCell group is configured with one or more SCells. The scheduled cell belongs to the PCell group when the scheduling cell belongs to the PCell group, and the scheduled cell belongs to the SCell group when the scheduled cell belongs to the SCell group.