The surface has been treated as perfectly smooth in the analysis of absorption of water vapor into falling film of aqueous lithium bromide solution. However, waves or disturbances begin to appear at Re_f of 20. In this paper, the influence of the waves is analyzed numerically by assuming sinusoidal wave motion over the falling film. The velocity profile inside the film is determined following Kapitza's analysis. The wave velocity and the wavelength are determined from Pierson and Whitaker's equations derived from the stability analysis. The wave amplitude is assumed to be 30% of the average film thickness. The liquid surface is immobilized by coordinate transformation and the basic equations are further changed to eliminate the cross derivative terms by Shyy et al.'s method. The results are compared with those for a laminar flow with a smooth surface. It is found that the absorption rates increase by a factor of 1.7-2.4 over the Re_f range of 20-100.