The present invention relates to a mobile communication system, and more particularly relates to a method for transmitting a small-sized control signal (also known as “small data”) using a control plane in a MTC (machine-type communication) service in a mobile communication system. In the present invention, MTC data is encapsulated in an existing control procedure or control message or the like, on a control signal, without performing packet data bearer setup, and the control signal having the encapsulated MTC data is sent between a network and a terminal, thereby optimizing network resource efficiency and reducing the wireless channel load.