Provided is a transmitter for a multi-input multi-output system including: a memory for storing a modulation system and power allocation coefficient for each antenna; a modulating unit for modulating data to be transmitted using the modulation system for each antenna stored in the memory when the data to be transmitted is input; and a power adjusting unit for adjusting the power according to the power allocation coefficient for each antenna stored in the memory to transmit the data to be transmitted, modulated at the modulating unit, via a corresponding antenna. A higher performance gain can be provided compared to a conventional open loop V-BLAST system by using a different modulation system and power for each antenna of a transmitter.