A method of transmitting a hybrid automatic repeat request, HARQ, acknowledgement/negative-acknowledgement, ACK/NACK, in a wireless communication system, the method performed by a user equipment, UE, and comprising: generating ACK/NACK bits for a plurality of downlink subframes related to a plurality of serving cells, wherein a number of the ACK/NACK bits is determined for the plurality of serving cells and the plurality of downlink subframes for which the UE needs to feedback ACK/NACK in each of the plurality of serving cells; arranging the ACK/NACK bits in an ascending order of cell indexes of the plurality of serving cells; generating encoded ACK/NACK bits by encoding the ACK/NACK bits; generating ACK/NACK symbols by modulating the encoded ACK/NACK bits; and transmitting the ACK/NACK symbols to a base station, characterized in that the ACK/NACK bits are arranged in order of a first series of ACK/NACK bits for a plurality of downlink subframes of a first cell having a lowest cell index and, appended at the end of the first series of the ACK/NACK bits for the first cell, a second series of ACK/NACK bits for a plurality of downlink subframes of a second cell having a cell index subsequent to the lowest cell index and, appended at the end of the second series of the ACK/NACK bits for the second cell, a third series of ACK/NACK bits for a plurality of downlink subframes of a third cell having a cell index subsequent to the cell index of the second cell, and, appended at the end of the third series of the ACK/NACK bits for the third cell, a fourth series of ACK/NACK bits for a plurality of downlink subframes of a fourth cell having a cell index subsequent to the cell index of the third cell, and wherein each series of the ACK/NACK bits includes at least two ACK/NACK bits for the downlink subframes of the corresponding serving cell and is ordered in ascending order of the downlink subframe indexes associated with each corresponding serving cell. generating ACK/NACK bits for a plurality of downlink subframes related to a plurality of serving cells, wherein a number of the ACK/NACK bits is determined for the plurality of serving cells and the plurality of downlink subframes for which the UE needs to feedback ACK/NACK in each of the plurality of serving cells; arranging the ACK/NACK bits in an ascending order of cell indexes of the plurality of serving cells; generating encoded ACK/NACK bits by encoding the ACK/NACK bits; generating ACK/NACK symbols by modulating the encoded ACK/NACK bits; and transmitting the ACK/NACK symbols to a base station, characterized in that the ACK/NACK bits are arranged in order of a first series of ACK/NACK bits for a plurality of downlink subframes of a first cell having a lowest cell index and, appended at the end of the first series of the ACK/NACK bits for the first cell, a second series of ACK/NACK bits for a plurality of downlink subframes of a second cell having a cell index subsequent to the lowest cell index and, appended at the end of the second series of the ACK/NACK bits for the second cell, a third series of ACK/NACK bits for a plurality of downlink subframes of a third cell having a cell index subsequent to the cell index of the second cell, and, appended at the end of the third series of the ACK/NACK bits for the third cell, a fourth series of ACK/NACK bits for a plurality of downlink subframes of a fourth cell having a cell index subsequent to the cell index of the third cell, and wherein each series of the ACK/NACK bits includes at least two ACK/NACK bits for the downlink subframes of the corresponding serving cell and is ordered in ascending order of the downlink subframe indexes associated with each corresponding serving cell.