We　present　a　polarization-multiplexing　off-axis　Mach-Zehnder　configuration　for　dual-wavelength　digital　holography　to　achieve　phase　imaging　in　one　shot.　In　this　configuration,　two　orthogonal　linear-polarized　waves　with　respect　to　different　wavelengths　are　employed　to　record　respective　holograms　synchronously,　where　two　recording　waves　transmit　independently　through　the　same　optical　paths　of　the　interferometer,　and　by　installing　two　analyzer　polarizers　each　to　filter　off　either　of　two　wavelengths,　and　filtering　through　the　other,　the　holograms　are　acquired,　respectively,　by　a　pair　of　CCDs　at　the　same　time.　The　unwrapped　phase　image　of　a　grating　with　groove　depth　7.1　mu　m　is　retrieved　via　spatial　frequency　filtering.