Optical absorption of nanometer-sized band-edge-modulated (BM) amorphous silicon-nitrogen (a-Si1-xNx:H) films, BM films, are discussed using the effective medium expression and characterized in terms of the optical gap E-g, the value of the slope in Tauc plot B, the Urbach energy E-u and the refractive index no as functions of the modulation period L and their correlations between them. E-g in BM film increases with decreasing L without changing n(0), i.e., average composition in the film. This results in the quantum-size effect. The values of B are hardly affected by L, while E increases with decreasing L. The increase in E is not expected from the effective medium expression and attributed to the effect caused by the sinusoidal modulation of the band-edge. (C) 2002 Elsevier Science B.V. All rights reserved.