We report magneto-optical Kerr microscopy study of the magnetic reversal behavior of Fe3Si/GaAs(100) epitaxial thin films grown by molecular beam epitaxy. Results are described in the context of superconducting quantum interference device and Kerr effect vector magnetometry to study the magnetic switching behavior. By tuning the Fe concentration of the samples from 75% to 83%, we found that the ratio of uniaxial to cubic anisotropy constants γ (= |Ku/K1|) would tremendously vary from 0.06 to 0.3. When the field was applied along the easy axis of Fe3Si samples, a step feature was observed in the M-H loops. This feature has been resolved in the domain image by Kerr microscopy, in which we observed a two-switching behavior at the field where the step feature occurred. These can be qualitatively understood by considering the ratio γ.