In this thesis, completely green 'sustainable' fiber reinforced composites were fabricated using biomass. A biobased thermoset resin was developed from a non-edible waste starch source obtained from mango processing industry and further reinforced with microfibrillated cellulose and sisal fibers to form a hybrid composite. Starch was obtained from the defatted mango seed kernel (DMSK) cake using simple filtration process. The mango seed kernel (MSK) starch was crosslinked using a benign crosslinker 1,2,3,4-butane tetracarboxylic acid (BTCA) using two different catalysts, sodium propionate (NaP), a novel green catalyst, and the currently used sodium hypophosphite (SHP). Properties and characteristics of the crosslinked resin prepared using the two catalysts were studied and compared. To improve the resin strength, it was crosslinked and reinforced with a commercially available microfibrillated cellulose (MFC). MFC was completely homogenized with water and starch in order to achieve good dispersion of MFC in the starch. It was observed that with the increase in the MFC content, the tensile properties of the resin improved. Further, sisal fibers were modified using a combination of alkali treatment and drying under tension to enhance their tensile properties. Alkali treatment removed hemicellulose and lignin keeping pure cellulose that results in better adhesion with the starch. Hybrid unidirectional composites were fabricated using the strength-enhanced sisal fibers, MFC and the crosslinked MSK starch. The final hybrid composites fabricated showed Young's modulus of about 8.5 GPa and tensile strength of around 165 GPa. While these composites are inexpensive, they can replace wood and wood based products such as particle boards, wafer boards, medium density fiber boards. The MSK resin can be used in place of petroleum based resins such as epoxy, polypropylene, etc., as well as edible starch and protein based resins.