Disclosed are a method and an apparatus for feed back of channel state information. The method for transmitting channel state information comprises the steps of: receiving a null data packet (NDP) frame; calculating signal to noise ratio (SNR) information based on subcarrier information of at least one spatial stream via which the NDP frame is transmitted; and calculating a compressed beamforming feedback matrix including channel state information based on the information on the subcarrier used in transmitting the spatial stream. Thus, accurate feedback information is calculated from a frequency selective channel and utilized to enable the efficient utilization of frequency resources.