The relationship between the structure and the optical properties of isotactic polypropylene (PP) containing 1,3:2,4-di-p-methylbenzylidene sorbitol (MDBS) has been studied. It is found that thinner injection-molded plaques of PP/MDBS show higher levels of transparency than compression-molded plaques. The enhanced molecular orientation in the skin layer is responsible for the depression of light scattering because of polarizability fluctuation, i.e., orientation fluctuation in the crystalline phase, because the size of the fluctuation becomes larger than the wavelength of visible light. Further, the crowded network structure of the MDBS fibers generated in molten PP prohibits spherulite formation and, as a result, depresses the spatial size of polarizability fluctuation in the core, which is smaller than the wavelength of visible light. Consequently, light scattering from the core layer is also reduced.