The effects of twin-screw extrusion processing conditions upon the formation of polypropylene/titanium dioxide (PP/TiO2) nanocomposites are investigated. To prepare PP/TiO2 nanocomposites by limiting the problem of filler dispersion at the nanoscale, an original method was developed based on the creation of TiO2 through hydrolysis-condensation reactions (sol-gel method) of titanium n-butoxide precursor during PP extrusion. The feed rate, the screw speed, and the amount of inorganic precursor were varied independently. The conversion rate of precursor as a function of process parameters was quantified by gas chromatography and mass spectroscopy combined techniques through the assessment of the alcohol formed. The effects of processing conditions on the development of the sol-gel reaction have also been investigated by using numerical simulations. The comparison between experimental and theoretical results shows that this simulation approach is relevant to predict the conversion of the inorganic precursor to TiO2 through hydrolysis-condensation reactions in molten PP. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 2174-2184, 2011