Dielectric spectroscopy is a technique which is still hardly used for on-line characterization of polymers. in this article we describe its use at medium frequencies (between 10 Hz and 1 MHz) for on-line monitoring of the morphology of polymer blends during extrusion. A sheet extrusion die containing two electrodes, made it possible to perform the dielectric on-line analysis. A blend of a thermotropic Liquid Crystalline Polymer (LCP) dispersed in polypropylene was used to follow the change in shape and co-continuity of the LCP phase with increasing extrusion speed. The creation of a more fibrous structure at higher shear rates was demonstrated by the dielectric technique as well as by SEM analysis. A blend of a thermotropic liquid crystalline polymer dispersed in polystyrene was chosen to study the evolution of the size of the LCP inclusions with increasing extruder speed. The Bottcher-Trukhan relation enabled us to convert the dielectric data to values of the particle size and a decrease in size with increasing shear rate was found. This was confirmed by SEM micrographs. The experiments and analysis presented in this article show that dielectric spectroscopy proves to be a valuable tool for on-line characterization of the microstructure of polymer blends.