Abstract: This paper studies multistage partial parallel interference cancellation for CDMA systems over multipath fading channels. By analysis of the variance of residual interference, we derive an expression determining the optimal interference cancellation weight in the event of channel estimation error and propose a channel-estimator-aided partial parallel interference cancellation applicable to multi-rate CDMA systems. The simulation results verify the reasonable assumption that the proposed partial parallel interference cancellation has performance better than partial parallel interference cancellation with freewill constant weight. It is indicated that, at a BER of 0.01, the performance loss of the proposed PPIC stage 2 is only 1.5 dB, compared to partial parallel interference cancellation with channel-known interference of one stage.