The polymer melt flow can be studied in-line using simultaneous rheo-optical techniques. The rheological behavior is obtained recording the pressure drop along the slit-die. Optical effects like light scattering and structure anisotropy are measured as turbidity, birefringence and low angle laser light scattering (LALLS). For this purpose we have designed and constructed an instrumented slit-die with three ports to measure pressure drop along the slit and two transparent windows for the optical measurements. It includes measuring turbidity and birefringence in the first window and LALLS at the second. The morphology of flowing polymer blends and composites are evaluated in the molten flowing field using, i) a known flowing field produced by a Cambridge Shearing System and ii) during extrusion in a Werner & Pfleiderer ZSK 30. Using different polymer blends and processing conditions the rheo-optical variables can be obtained and the morphological characteristic of the polymer flow be studied. The results can be compared with any conventional off-line measurement like, thermal (DSC), spectroscopic (FTIR) and morphology (POM, SEM, TEM), taken from samples collected during extrusion. Examples of various set of data will be presented during the conference, including diluted polymer blends and composites.