The acoustic velocity in a nonequilibrium wet steam flow has been investigated theoretically. Modified equations of unsteady one -dimensional wet steam flow are taken to describe the propagation of a plane pressure wave of very small amplitude through the wet steam flow. These equations are derived for the conditions of nucleating and non-nucleating wet steam assuming that the vapour phase obeys the perfect gas law and the water and vapour phases are in disequilibrium both thermally and dynamically. The acoustic velocity is shown to depend mainly on the steam wetness, flow non-equilibrium characteristics (i.e., vapour supercooling and slip ratio) and flow pressure; while it slightly affected by the size of droplets and nucleation occurrence.