In this paper a cumulant-based beamforming technique for synchronous CDMA system with decorrelator is presented. With a decorrelating detector the proposed algorithm has the advantages that the steering vector of desired user's can be estimated independently by eliminating all the other resolved signal interferences. Furthermore employing a cumulant-based signal processing technique the steering vector of the decoupled signals can be estimated blindly. Simulation results show that the cumulant-based beamformer demonstrates excellent performance.