A prototype on-line rotational rheometer was fixed between a twin screw extruder and a multi-rod die of an industrial pelletization line used for the manufacture of polymer-clay nanocomposites. After diverting the required amount of melt to the device, measurements were performed in small amplitude oscillatory shear and used to estimate the level of dispersion of the organoclay in the polypropylene matrix, by means of correlations that are commonly utilized. The aim is to determine whether changes in clay type, clay content, feed rate and screw speed cause detectable alterations in the rheological response and thus in the level of dispersion, with a view to practical process monitoring and control. The analysis of the data is supported by XRD and electron (scanning and transmission) microscopy observations.