Based on the Maximum-Likelihood (ML) criterion, this paper proposes a novel noncoherent de-tection algorithm for Orthogonal Multicode (OM) system in Nakagami fading channel. Some theoreticalanalysis and simulation results are presented. It is shown that the proposed ML algorithm is at least 0.7 dBbetter than the conventional Matched-Filter (MF) algorithm for uncoded systems, in both non-fading and fad-ing channels. For the consideration of practical application, it is further simplified in complexity. Comparedwith the original ML algorithm, the simplified ML algorithm can provide significant reduction in complexitywith small degradation in performance.