We are concerned on the phase transition of mixing zone in the zero Mach number limit of compressible twophase flow. In the transitional regions, formal asymptotic expansions are derived for the solutions of compressible equations. Specifically, under the singular limit process, the slow and fast transitional variables are found away from the initial time and near the initial time, respectively.

transition layers, singular perturbation, zero Mach number limit, asymptotic expansions, twophase flow equations.