In this paper, we presented a new interference suppression method based on groupwise decorrelation for the multirate wideband-code division multiple access (W-CDMA) downlink. Code grouping in the proposed method is performed according to the correlation property between the mother code and the child code in the orthogonal variable spreading factor (OVSF) code tree. The decorrelation process based on the grouped codes, so called groupwise decorrelation, is then performed to suppress the interference induced in the downlink propagation. We demonstrate that the proposed method can enhance the performance significantly, with lower computational complexity and higher operational efficiency in which any information about interference users (code, data, amplitude) is not required to know in prior at the detection stage.