Abstract <p>Oligomeric poly <i>Brassica juncea</i> oil fumarate (o-PMF) polyester composites have been created by combining fumarate resin and agave sisalana fibers. The polyester composites were characterized using FT-IR, swelling coefficient, crosslink density, solvent absorptivity percentage and thermal analysis. The mechanical parameters of the composites were examined, including tensile strength, young’s modulus, shore A hardness, and elongation at break. The specimens for the aforementioned tests were prepared according to ASTM standards. The fiber reinforced polyester composites improved the mechanical characteristics of polyesters, and the surface morphology of the polyester was examined using a scanning electron microscope. The results of the investigations demonstrated that the newly created cross-linked poly brassica juncea oil fumarate polyesters are prospective biodegradable materials for various consumer applications such as package materials, automobile, pharmacy and agricultural applications.</p>