Lactic acid based thermoset were synthesised by reacting lactic acid with glycerol and functionalizing lactic acid branches by methacrylic anhydride. Resins with different chain length were prepared and their thermo mechanical properties were examined through DMA analysis and their molecular structures were analyzed by NMR method and their viscosity were investigated through rheometry analysis and three monomers were selected as the best chain length. Degree of reaction in different reaction times was evaluated by a modified titration method and bulk preparation of resin was performed by optimal process condition. DSC analysis was conducted in order to evaluate curing behaviour of resin with benzoyl peroxide as cross-linking initiator. TGA analysis was performed to check thermo stability of the resin. Bio composites by viscose unidirectional and bidirectional knitted fabrics and also non woven viscose fiber with different fiber loads were prepared by ordinary hand layup impregnation followed by compress moulding and their mechanical and thermo mechanical properties were characterized by tensile, flexural, charpy and DMA analysis and optimum fiber loads were identified for each fiber type. Ageing properties of prepared composites were examined by placing samples in climate chamber to simulate long time ageing and ageing experiment was followed by tensile and flexural test to evaluate mechanical properties after ageing simulation. Composite`s swelling properties for water and some other solvents were investigated and also their chemical resistance were evaluated by immersing them in 1M HCl and KOH. The resin was also compared with a commercial oil based thermoset by preparing glass fiber reinforced composites and also effect of adding styrene to the resin were evaluated. Results of this work demonstrated that the novel synthesised have very high mechanical and thermo mechanical properties surpassing commercial oil based poly esters but ageing behaviour is not very good however adding styrene can improve ageing properties. Also the resin is compatible with cellulosic natural fibers and forms strong composites.