The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for deactivating SCells upon a TAT expiry for PUCCH cell in a carrier aggregation system, the method comprising: configuring a first cell with Physical Uplink Control Channel (PUCCH) resource in a PUCCH group and in a Timing Advance Group (TAG) with a configured Time Alignment Timer (TAT), wherein the first cell and zero or more second cells belong to the PUCCH group, and the first cell and zero or more third cells belong to the TAG; starting the TAT of the TAG; and deactivating all cells belonging to the PUCCH group when the TAT expires.