This paper is concerned with the baud duration estimation of M-ary PSK signals with M=2, and 4. The baud duration is one of the important parameters to intercept, and recognize digitally modulated signals as well as to determine the optimum jamming for them. The proposed method for baud duration estimation is based on the computation of the spectral correlation function of a signal. The proposed method for baud duration estimation provides reliable and accurate results at weak SNR. It is found that, a good estimation for baud duration of M-ary PSK signals at the SNR of —5 dB is available. Also, in this paper a new method for fast computation of the spectral correlation function is provided.