An apparatus and method for transmitting/receiving data in a closed-loop multi-antenna system. A receiver receives a plurality of data streams from a plurality of transmit antennas of a transmitter, generates Channel Quality Information (CQIs) of channels that carry data streams transmitted from at least two transmit antenna allocated to the receiver among the plurality of transmit antennas, and transmits the CQIs to the transmitter. For the CQI generation, the receiver generates a channel matrix through channel estimation of the received data streams, generates a reception beamforming matrix from the channel matrix including only components of the data streams transmitted from the allocated transmit antennas, and calculates the CQIs using the channel matrix, the reception beamforming matrix, and a total signal-to-noise ratio (SNR) obtained through the channel estimation.