We demonstrate the distinctive optical properties of disordered nanostructures on glass substrates in accordance with changes in the average size of the nanostructures. Dissimilar sizes of nanostructures were fabricated by using different thicknesses of thermally dewetted Ag nanoparticles as etch masks. Unlike a flat glass substrate, the nanostructured glasses (NSGs) show a changed optical characteristic. By increasing the size of the nanostructures, the wavelength of the peak transmittance of about 99% gradually moved from 730 to 2000 nm. To clearly discern the effect of the different sizes of nanostructures, the normalized angle-dependent transmittance spectra of the NSGs were analyzed. Only if the size becomes relatively larger than the wavelength of the incident light are the transmittance spectra more strongly affected by the incident angle as well as by the relative size, rather than by the Fresnel reflection.