The present invention relates to methods for supporting carrier sensing in a wireless access system supporting an unlicensed band, and devices supporting same. A method for supporting carrier sensing in a wireless access system supporting an unlicensed band, according to an embodiment of the present invention, comprises the steps of: selecting a backoff counter value for performing carrier sensing; performing carrier sensing in a serving cell (S-cell) until the backoff counter value reaches a predetermined threshold value; when the backoff counter value reaches the predetermined threshold value, transmitting data in a transmission opportunity (TXOP) interval; receiving a reception state feedback indicating whether the transmitting of data is success, collision or error; and resetting the backoff counter value on the basis of the reception state feedback, wherein the S-cell can be configured in an unlicensed band.