This study describes the development and characterization of an experimental system employing laser-induced Rayleigh light scattering with digital data acquisition as a time-resolved quantitative concentration probe in the plane mixing layer of a binary gas. The scattered signal and noise levels are given. A maximum error of 4%, which is within the expected experimental accuracy of a typical Rayleigh scattering system, occurs in the interpretation of a Rayleigh scattering as gas concentration due to noise. It is showed that the laser Rayleigh light scattering technique provides measurements having high spatial resolution for various locations within the concentration flow field.