When used at oblique angles of incidence, the reflectance and transmittance of thin films exhibit strong polarization effects, particularly for the films inside a glass cube, which results from the fact that the tangential components of the electric and magnetic fields are continuous across each layer interface. However, for many applications, the polarization effects are undesirable and should be reduced. In the present paper, a method for designing a non-polarizing beam splitter (NPBS) in a cube is introduced, based on the Brewster condition. Applied examples of the NPBSs designed employing this method are also researched within specified wavelength ranges. Moreover, the effects of some important parameters, including the incident angle and the material indices, on the NPBS are investigated. Optical property simulations are presented.