The present invention relates to a wireless communication system. A method for transmitting channel state information (CSI) in a wireless communication system, according to one embodiment of the present invention, comprises steps of: subsampling a codebook for a four-antenna port including 16 precoding matrices; and performing feedback for the CSI on the basis of a subsampled codebook, wherein when a rank indicator (RI) is four, a subsampled codebook includes, from 16 precoding matrices, a first precoding matrix having index 0, a third precoding matrix having index 2, a ninth precoding matrix having index 8, and an eleventh precoding matrix having index 10.