A method of transmitting uplink control information in a wireless communication system, the method performed by a user equipment, UE, and comprising: receiving, from a first cell among a plurality of serving cells, a first uplink grant including a first piggyback indicator used for instructing the UE to piggyback both a first uplink transport block and the uplink control information of the first cell onto a target cell; receiving, from a second cell among the plurality of serving cells, a second uplink grant including a second piggyback indicator used for instructing the UE not to piggyback a second uplink transport block of the second cell onto the target cell; selecting the target cell on which the first uplink transport block and the uplink control information are to be piggybacked among the plurality of serving cells, based on the first piggyback indicator in the first uplink grant, wherein the target cell on which the first uplink transport block and the uplink control information of the first cell are to be piggybacked is selected among the plurality of serving cells, and the target cell satisfies one of three conditions including a first condition of having a highest priority, a second condition of being a primary cell, and a third condition of having a broadest bandwidth; multiplexing the first uplink transport block and the uplink control information of the first cell onto an uplink shared channel of the target cell; and transmitting, via the uplink shared channel, the uplink control information multiplexed with the first uplink transport block, to the target cell; and transmitting the second uplink transport block to the second cell based on the second piggyback indicator in the second uplink grant. receiving, from a first cell among a plurality of serving cells, a first uplink grant including a first piggyback indicator used for instructing the UE to piggyback both a first uplink transport block and the uplink control information of the first cell onto a target cell; receiving, from a second cell among the plurality of serving cells, a second uplink grant including a second piggyback indicator used for instructing the UE not to piggyback a second uplink transport block of the second cell onto the target cell; selecting the target cell on which the first uplink transport block and the uplink control information are to be piggybacked among the plurality of serving cells, based on the first piggyback indicator in the first uplink grant, wherein the target cell on which the first uplink transport block and the uplink control information of the first cell are to be piggybacked is selected among the plurality of serving cells, and the target cell satisfies one of three conditions including a first condition of having a highest priority, a second condition of being a primary cell, and a third condition of having a broadest bandwidth; multiplexing the first uplink transport block and the uplink control information of the first cell onto an uplink shared channel of the target cell; and transmitting, via the uplink shared channel, the uplink control information multiplexed with the first uplink transport block, to the target cell; and transmitting the second uplink transport block to the second cell based on the second piggyback indicator in the second uplink grant.