Provided is a channel status information (CSI) transmission method performed by a user equipment in a carrier aggregation system. The method includes: allocating a plurality of serving cells; configuring a subframe predetermined to transmit CSI for a single serving cell among the allocated plurality of serving cells; and if uplink data transmission via a physical uplink shared channel (PUSCH) region exists in the configured subframe and if the single serving cell is deactivated, transmitting deactivation confirmation information for indicating that the single serving cell is deactivated via the PUSCH region together with the uplink data.