The present specification proposes a technique for controlling a deactivation timer of a cell. Specifically, the present specification proposes a method for controlling a deactivation timer of a cell in a mobile communication system. The method comprises the steps of: configuring a primary cell and at least one secondary cell on user equipment (UE); receiving, from the UE, an indicator related to a deactivation timer for one secondary cell from among one or more secondary cells; and disabling, on the UE, the deactivation timer of one secondary cell on the basis of the indicator.