In this paper, we analyze the distribution of the envelope of the received signal over frequency-nonselective slow Rician fading channels with aadditive white Gaussian noise(AWGN). Especially, we can obtain the error rate performance of noncoherent M-ary FSK(MFSK) over slow and flat Rician fading channels and AWGN from the new probability density function(PDF) of the envelope, not PDF of the instantaneous signal-to-noise ratio(SNR) published before, of the received signal. When coherent MFSK signals experience the Rician fading channel, the performances are derived, using the union bound.