A new valorization strategy for Olive Solid Waste (OSW) has been carried out which consists in incorporating this biomass as a filler in a biopolymer matrix. The aim of the present work is to gain a fundamental understanding of the relationships between structure, processing conditions and final properties of the obtained materials. In this study, biocomposites based on poly(D,L-lactide) (PDLLA) and two OSW fillers were prepared with various filler contents. It was highlighted that the inclusion of OSW under elevated temperatures resulted in the degradation of the matrix leading to a reduction of the viscoelastic properties and molar masses. Nevertheless, it was demonstrated that this degradation of the PDLLA matrix could be attenuated through two approaches. The first was chemical and consisted in using a chain extender agent named Joncryl containing glycidyl methacrylate (GMA) functions. The second route was physical and consisted in coating the OSW with the hydrophobic biopolymer poly(ε-caprolactone) followed by mixing with PDLLA. Indeed, the processing conditions were monitored to produce composites with well controlled properties. The effect of OSW with and without Joncryl on the thermal stability as well as the melt and the crystallization properties was assessed. Furthermore, the rheological properties in linear viscoelasticity of the controlled systems PDLLA/OSW/ Joncryl and/or PDLLA/ (OSW) coated with PCL were investigated in the molten state. The improvement of the shear viscoelastic properties corroborated the measured molar masses. The physicochemical matrix/filler interactions had to be taken into account to explain the improved rheological, morphological and mechanical properties. The obtained materials with a tailored properties were fully recovered by two forming process as well extrusion and injection molding.