A method is provided for transmitting downlink data in a wireless access system. An evolved Node B (eNB) transmits a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled. The eNB transmits, via a physical downlink control channel (PDCCH), downlink control information (DCI) for scheduling a physical downlink shared channel (PDSCH). The eNB transmits, via the PDSCH, downlink data based on the DCI. The eNB has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to 256QAM. The downlink data is encoded based on the first MCS index table even though the second MCS index table has been enabled, when a format of the DCI is a DCI format 1A and the DCI format 1A has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).