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 μm is retrieved via spatial frequency filtering.