Abstract: A method of transmitting data using HARQ includes transmitting a first block, a partial bit stream of a codeword, and transmitting a second block, a bit stream starting from a bit index next to the last bit index of the first block, according to a retransmission request with respect to the codeword, wherein a different modulation scheme from that of the first block is applied to the second block. A coding gain of an incremental redundancy (IR) mode can be obtained although the amount of retransmission data is arbitrarily changed according to a change in transmission attributes such as a modulation scheme, resource allocation, the size of a transport block, or the like, in the adaptive HARQ scheme, so the transmission efficiency of a system can be enhanced.