The present invention relates to a transmission time interval (TTI) bundling method in wireless access systems and to an apparatus for same. In particular, the TTI bundling method includes the following steps: a terminal receives information indicating the bundling size value from a base station; the terminal automatically re-transmits packets through a predetermined number of TTIs following four TTIs without the reception of Acknowledgement/Negative-ACK (ACK/NACK) information for the packets from the base station; the terminal receives the ACK/NACK information for the packets from the base station; and the terminal retransmits packets in a Hybrid Automatic Repeat and Request (HARQ) scheme when receiving the NACK, wherein the predetermined number of TTIs is determined according to the bundling size value.