The general probability of error expressions of coherentM-ary PSK (M = 2, 4, 8, 16) systems in the presence of both impulsive and Gaussian noise are derived. This work is an extension of our paper related to BPSK and DPSK systems in a complex interference environment . The presented impulsive and Gaussian channel disturbance is a first-order approximation to operational multichannel satellite and terrestrial microwave systems in which, in addition to front-end Gaussian noise, out-of-band intermodulation noise may be present. Our analysis contains an extension of the method developed by Bello and Esposito , , to include the Gaussian as well as the impulsive noise environment. The numerical results show that a well defined threshold region exists, above which the effect of the impulsive noise on the system performance is predominant.