Rheology of filled polymeric systems is an ever expanding area for industrial researchers. New experimental propylene-ethylene copolymers supplied by The Dow Chemical Company have a unique chain microstructure and an excellent balance of product performance properties. They feature narrow molecular weight distribution and broad crystallinity distribution. The unique molecular architecture offers the distinguishing feature of allowing exceptionally high filler loadings (even higher than 80wt%) yet maintaining good processability. Our goal is to thoroughly characterize the rheological behavior and the interfacial phenomena to provide a fundamental understanding of the lower than expected viscosity. Such a fundamental understanding is necessary for the design of other new resins with a better capacity for incorporating particles and for the development of optimum processing conditions for the composites.  In this work, the rheological properties of experimental P/E copolymers filled with calcium carbonate are studied. Steady shear and dynamic measurements on composites with different loadings (0-80wt%) are carried out