The present invention relates to a wireless access system supporting machine type communication (MTC), and to various methods for an MTC terminal transmitting/receiving data. A method for an MTC terminal receiving data in a wireless access system supporting MTC, as one embodiment of the present invention, may comprise the steps of: receiving a modulation and coding scheme (MCS) index indicating a MCS, and a physical resource block (PRB) index indicating the size of a PRB allocated to a MTC terminal; checking a transport block size (TBS) index that is mapped with the MCS index and deriving a TBS on the basis of the TBS index and the PRB index; and on the basis of the TBS, decoding a physical downlink shared channel (PDSCH) in order to receive data. Here, the size of the MCS index is configured to be a 4-bit size, and the TBS index may be configured so as to support only from 0 to 9 for the MTC terminal.