A method and a device for transmitting channel state information (CSI) in a wireless communication system are provided. A terminal performs a measurement on the basis of at least one beamformed CSI reference signal (RS) resource, and transmits, to a base station, the CSI and information relating to preferred beam on the basis of the measurement result, wherein the CSI includes a precoding type indicator (PTI), and the PTI indicates whether the measurement is based on a CSI RS resource which is not precoded, or is based on the beamformed CSI RS resource.