Enhancement of the Kerr effect was studied to assess its effectiveness in improving readout characteristics of a magneto‐optical memory utilizing MnBi films. SiO was used to enhance the Kerr effect by coating it on magnetic films. The coating results in a change, not only in the Kerr rotation but also in the ellipticity and reflectivity of the films. Changes of these quantities were calculated as a function of the SiO thickness, using optical constants of both MnBi and SiO, i.e., the refractive indicesn2andn3of SiO and MnBi, respectively, and the off‐diagonal element &egr;′ of the dielectric tensor of MnBi. The optical constants determined in this work weren2=(2.0±0.02)−(0.02±0.02)i,n3=3.1−3.5i, and &egr;′ = −1.2−0.4iat a wavelength of 6328 Å. The Kerr rotation and the reflectivity were measured for various SiO thicknesses and were compared with the results of theoretical calculations. Experimental and theoretical results agreed well with each other. The readout signal‐to‐noise ratio, which is a function of the Kerr rotation, ellipticity, and reflectivity, is expected to be improved by a factor of more than 2, when SiO is coated on the MnBi film surface.