We employed the integral equation method (IEM) to simulate optical scattering by a randomly rough surface for spectroscopic ellipsometry. An explicit Mueller-matrix expression of the IEM for single scattering by moderately small surface roughness makes it possible to calculate the depolarization effect. The IEM allows a relatively rigorous assessment of the surface-scattering effect in a wide spectral range. (C) 2003 Optical Society of America.