A method of uplink control information transmission for a mobile device with carrier aggregation in a wireless communication system is disclosed. The method comprises being configured a plurality of cells including a primary cell and at least a secondary cell by a network of the wireless communication system, determining to transmit the uplink control information in a transmission time interval, and when the primary cell has no uplink resource for the uplink control information transmission, transmitting the uplink control information on at least a secondary cell having uplink resources in the TTI.