PMMA and PMMA films doped with different contents of azo dye have been made by using the casting technique. The absorption spectral analysis showed that the doped films have two absorption bands attributed to the pi-pi* and pi-pi* transition of chromophore groups. These bands disappear upon UV-irradiation, suggesting that the studied system undergoes a photo degradation process. The absorption coefficient and optical energy gap (E-g) have been obtained from the absorption edge in the 200-900 nm range. It was found that Eg decreases with increasing doping levels, whereas it increases with increasing irradiation time. The width of the tail of localized states in the band gap (Delta E) was evaluated using the Urbach edge method. Some optical parameters were determined from the reflection and transmission spectra in the spectral range of 200-2500 nm. The dependence of the refractive index on irradiation time and doping level have been discussed. It was found that the photo-induced refractive index changes are very large. These changes suggest the applicability of the studied system in optical devices. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1416-1423, 2010