The aim of this work was to study the variation of processing properties, structure and properties of highly filled natural fillers polymer composites (HNFPC) undergo several reprocessing in a molten state. These type of materials, frequently used by the production of various products, ought to be recycled after the end of its life time, accordingly to nowadays regulations. Thermoplastic polymers like polyethylene, polylactide, polypropylene and poly(vinyl chloride) were applied as matrix. The composites were filled with various natural fillers like wood flakes, flex, hemp, etc. Two contradictory effects were found during multiprocessing of HNFPC. The first one is a general improvement of certain properties due to better homogeneity of the composite materials, and second the macromolecular degradation induced lowering of application properties. The multi-processing induced “modification” of processing properties like changes of the molten flow viscosity will be presented and discussed. These results will be complemented by structure investigations (particularly changes of the length of fillers and its distribution in polymeric matrix) and properties resultant from these changes. The structural effects appearing along with the multi-processing will be explained by the determination of the degradation energy.