Structural, magnetic and magneto-optical properties of polycrystalline bismuth iron garnet Bi3Fe5O12 (p-BIG) films were prepared on Bi1.7Y1.2Fe5.1O12 coated glass. The p-BIG layers were formed on vitreous SiO2 and Coming 0317 glass substrates by rf-sputtering in the wide range of substrate temperature from 475°C to 700°C. BIG single crystal (s-BIG) films were also prepared on gadolinium gallium garnet (GGG) single crystals in the temperature range from 500°C to 600°C. It is found that p-BIG layers could be obtained by sputtering with Ar gas alone as well as mixed gases of Ar and O2, and that they show higher figures of merit than s-BIG layers because of small absorption of light for the wavelength of around 540nm. The effect of glass substrates on the crystallinity, magnetic and magneto-optical properties of the p-BIG films were also investigated.