Disclosed is a method for effectively forming uplink control information transmitted through a downlink from a base station to a terminal in a mobile communication system for providing a packet service and transmitting the uplink control information with minimum radio resources occupied. The method includes generating uplink control information; allocating the uplink control information to a downlink-shared radio resource for packet data transmission based on downlink scheduling information; and transmitting the radio resource to a terminal. The present invention is applied to a mobile communication system.