This paper is an extension of the previous work of Rahman and Sesay (see Proceedings of IEEE Canadian Conference on Electrical and Computer Engineering, Halifax, Canada, p.245-49, 2000) where they evaluated the performance of a non-coherent MT-CDMA system using differential binary phase shift keying (DBPSK) modulation. Here, we investigate the performance of the same system using diversity combining. The paper presents the theoretical analysis in terms of the average bit error rate (BER). The study is carried out for a slowly Rayleigh fading and frequency selective channel in an indoor environment using M-branch post-detection diversity combining. The influences of the diversity order and number of tones are studied here, for a given bandwidth (BW), bit rate and transmitter power. The analysis and supporting simulation work show that the post-detection diversity provides significant BER improvement over non-diversity reception for a non-coherent MT-CDMA system.