The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for reporting CSI in a wireless communication system, the method comprising: a step for configuring a plurality of serving cells; and a step for reporting the CSI of only one serving cell in a corresponding subframe, wherein the step for reporting the CSI of only one serving cell comprises: excluding reporting the CSI of a lower priority when CSI reports of the plurality of serving cells in the corresponding subframe collide; and excluding reporting the CSI of serving cells other than the serving cell having the smallest index when the CSI reports of different serving cells having the same priority in the corresponding subframe collide.