In order to obtain a more accurate dispersion relation for the optical properties of amorphous Si (a-Si) films, a modification on Forouhi-Bloomer's model (FB model) considering the effects of the non-parabolic bands and phonons was performed. A series of experimentally measured optical constant data have been fitted by the modified and original FB models for asserting the advantages of the former. The results indicates that considering the non-parabolic conduction and valence bands for modeling the optical properties of the a-Si films improves the goodness of fits and the modified model provides more useful and correct information about the optical properties. (c) 2006 Elsevier B.V. All rights reserved.