Embodiments of the present disclosure relate to secondary cell activation. A method comprises transmitting, from a first apparatus and on a serving cell in an active status, a MAC layer command for activating at least one secondary cell to a second apparatus, the MAC layer command indicating a configuration on a procedure for activating the at least one secondary cell. The method further comprises receiving an acknowledgement for the MAC layer command from the second apparatus. The method further comprises causing the second apparatus to synchronize, based on at least the configuration and the acknowledgement, with the first apparatus on the at least one secondary cell. As such, the time for activating a Scell can be greatly shortened.