This paper introduces a novel analytical approach for monitoring the degree of condensation of thin siloxane films, which is potentially suitable for in-line process control during the deposition of such layers, e.g., to polymer films. Near-infrared (NIR) reflection spectroscopy in combination with chemometric methods was used as a process monitoring tool. The state of the formation of the inorganic SiOSi network in partially condensed 3-methacryloxypropyltrimethoxysilane batches was analyzed by inverse gated Si-29 NMR spectroscopy. Results were expressed in terms of different relative ratios of the Ti species (i.e., structures with different numbers of SiOSi units per Si atom). These data were used for calibration of the NIR method, which was applied to thin layers printed on a polymer foil with a thickness of similar to 2.2 g m2. The root-mean-square error of prediction (RMSEP) for the determination of the ratio of the Ti species from the NIR spectra was found to be less than 3%. The error of the reference data from 29Si NMR spectroscopy is 4%, which results in an overall error of 5%. Moreover, the thickness of siloxane layers was determined by this method in a range from 2.5 to 5.5 g m(2) using gravimetry for calibration (prediction error similar to 0.3 g m(2)).