Provided are a method and an apparatus for transmitting acknowledgement/non-acknowledgement (ACK/NACK) of a terminal in a carrier wave aggregation system. The method comprises: receiving a UL grant by a subframe n−k1 of a first serving cell, wherein the UL grant comprises uplink allocation and piggyback information, wherein the piggyback information indicates the number of first physical downlink shared channels (PDSCHs) scheduled before the subframe n−k1; attempting a detection of a second PDSCH by a subframe n−k2 of a second serving cell; and transmitting an uplink transmission block and ACK/NACK information through a physical uplink shared channel (PUSCH) on the basis of the uplink allocation by subframe n, wherein n, k1 and k2 are constants, k1>k2, and the ACK/NACK information may comprise a first ACK/NACK according to the piggyback information, and a second ACK/NACK corresponding to the detected second PDSCH.