Abstract: A decision-theoretic based scheme is developed for modulation classification in a fading environment. The proposed method takes into account a flat Rayleigh fading propagation channel. The likelihood function is derived according to the channel and signals parameters character and classifier is constructed. Spatial diversity technique with multi-antennas array receiver is exploited to improve the correct classification probability. A method dealing with the effect for diversity induced by the displacement of receiving antennas is also proposed. Simulations demonstrate that the proposed scheme is efficient in fading situations.