The depolarized light mixing (DLM) system is presented as a useful device in light beating spectroscopy for the observation of molecular rotation, deformation, and reaction which accompany an anisotropic change of polarizability. The system has the following merits: (1) Doppler broadening does not appear because it observes forward scattering; (2) only the line shape coming from a pure anisotropic polarizability change is obtained; (3) it can work automatically as an optical heterodyne system with the stray light from the second polarizer serving as a local oscillator light; (4) there is no difficulty in matching the wavefronts of the scattered light and local oscillator beam; and (5) the scattering volume can be made large without diminishing the efficiency of light beating. These characteristics are described through the numerical evaluation of beating efficiency and signal‐to‐noise ratio.