The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very significant downlink multiple access technique for high-rate data transmission in the fourth generation wireless communication systems. Throughput maximization of MC-CDMA systems is a major fundamental issue. In this paper an improved algorithm is proposed which will result in optimum maximization of the throughput for the given Channel state information (CSI). Proposed algorithm gives the modified technique of sub channel allocation in the downlink transmission of MC-CDMA systems. Simulation results shows that proposed algorithm gives far better results than the original algorithm.