The tensile and flexural properties of new thermosetting composites made by the free radical polymerization of natural oil-based resins reinforced with natural fillers have been determined for various oils, fillers, and resin compositions. Tung, and conjugated corn, soybean, linseed, and fish oils have been co-polymerized with varying amounts of divinylbenzene (0-15 wt %), dicyclopentadiene (0-10 wt %), n-butyl methacrylate (20-35 wt %), and maleic anhydride (0-15 wt %). The natural fillers used include widely produced and underused agricultural residues, such as sugar-cane bagasse, soybean, rice, and oat hulls, as well as residues from the wood industry, such as wood flours and wood fibers. The thermal stability of the new materials has been determined by TGA and the wt % of monomer incorporation has been calculated after Soxhlet extraction and analysis of the extracts by 1H NMR. Scanning electron microscopy of selected samples revealed improvement on the filler-resin interaction for samples containing maleic anhydride. Composites with Young's modulus and tensile strength as high as 4.3 GPa and 17.6 MPa, respectively, have been prepared. The materials obtained show promising application in the automotive, aerospace and housing industries as decorative, light-weight panels. The conjugation of the oils used in this study involves the use of an efficient homogeneous Rh catalyst that is completely discarded after the reaction. The conversion of that catalyst into a biphasic system can turn this reaction into an economically viable, and greener process. In the present work, we have optimized the conversion of the homogeneous catalyst [RhCl2(C8H14)2]2 into a complex that works under biphasic conditions for the conjugation/positional isomerization of carbon-carbon double bonds. A maximum yield of 96% has been obtained at optimal conditions using soybean oil as the substrate.