Several multiuser detectors have been recently proposed to combat multiple-access interference and near-far problem for CDMA systems. The performance of a multi-user receiver in combining the decorrelating decision-feedback scheme for a synchronous DS/CDMA system is considered. Using the Gaussian approximation on the multiple-access interference and amplitude estimation errors, we derive a closed form expression for the BER performance of the decorrelating decision-feedback detector in single-path Rayleigh fading channel and power controlled system. And, we show that our analysis agrees with the results of simulations. A modified decision-feedback detector is also proposed and analyzes. Numerical results show that the modified dicision-feedback detector proposed in this paper results in enhanced performance.