In this paper, we investigate the impact of feedback delay and channel estimation error (CEE) on the performance of wireless multi-user decode-and-forward (DF) relay systems in independent and non identically distributed Rayleigh fading channels. To assess the performance, we derive the exact probability density function (PDF) expression of the signal-to-noise ratio (SNR) for each link, and the average outage probability expression with imperfect channel state information (ICSI). Numerical results are presented to confirm the analytical expressions and to investigate the effect of the ICSI on the performances of the wireless cooperative system.