Thin films were fabricated from poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) based on hydrogen bonding layer-by-layer (LBL) assembly process. Due to light interference, PVPON/PAA films present Fabry-Perot fringes in die UV-Vis-NIR spectrum. LBL assembly constructed the film on both sides of substrate (double-side film), which are different to traditional vacuum deposition that forms the film only on one side of substrate (single-side film). The light interference processes of the double-and single-side films were fully analyzed. Using the peak positions and amplitude of the Fabry-Perot fringes, the refractive index and thickness of the film can be evaluated. Furthermore, Fabry-Perot fringes can be utilized to monitor the film's growth and water content variation in the film. (c) 2007 Elsevier B.V. All rights reserved.