The present invention relates to a broadband wireless access system including a relay station, and more particularly to an efficient procedure of Automatic Repeat Request (ARQ) operations in a relay station and an apparatus for performing the same. A method for transmitting data for at least one terminal (AMS) from a base station (ABS) to a relay station (ARS) in the broadband wireless access system according to an embodiment of the present invention comprises the steps of generating second transmission unit data using a plurality of first transmission unit data to which different relay sequence numbers are assigned; and transmitting the second transmission unit data to the relay station. The second transmission unit data can be transmitted through the same tunnel as the first transmission unit data.