Abstract: Based on the theory of scalar diffraction,the diffraction of a uniform plane wave at two asymmetrical rectangular apertures is studied analytically and numerically. The transversal,on-axis and off-axis intensity distributions of the Fraunhofer and Fresnel diffraction are given and analyzed. It is shown that the Fraunhofer and Fresnel diffraction can be distinguished by the relative error of their maximum intensity. The result is consistent with that for the case of two circular apertures.