The morphology of polymer nanocomposites is usually characterized by various methods like X-ray diffraction (XRD) or transmission electron microscopy (TEM). In this work, a new approach for characterizing nanocomposites is developed: the results of small angle x-ray scattering, on-line extensional rheometry (level of melt strength) and Young's modulus out of tensile test are correlated with those of near infrared (NIR) spectroscopy. The disadvantages of the common characterization methods are high costs and very time consuming sample preparation and testing. In contrast, NIR spectroscopy has the advantage to be measured in-line and in real time directly in the melt. The results were obtained for different aggregate states (NIR spectroscopy and on-line rheotens test in melt state, tensile test, and XRD in solid state). Therefore, important factors like crystallization could not be considered. Nevertheless, this work demonstrates that the NIR-technology is perfectly suitable for quantitative in-line characterization. The results show that, by the installation of a NIR spectrometer on a nanocomposite-processing compounder, a powerful instrument for quality control and optimization of compounding process, in terms of increased and constant quality, is available. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3047-3053, 2010