Polylactide (PLA), which is one of the most important biocompatible polyesters that are derived from annually renewable biomass such as corn and sugar beets, has attracted much attention for automotive parts application. The manufacturing method of PLA is the ring-opening polymerization of the dimeric cyclic ester of lactic acid, lactide. For the PLA composites including stereocomplexed with L- and D-PLA, we developed the unit processes such as fermentation, separation, lactide conversion, and polymerization. We investigated D-lactic acid fermentation with a view to obtaining the strains capable of producing D-lactic acid, and through catalyst screening test for polycondensation and depolymerization reactions, we got a new method which shortens the whole reaction time of lactide synthesis step. Poly(d-lactide) is obtained from the ring-opening polymerization of d-lactide. Also we investigated several catalysts and polymerization conditions. Finally, we got the best catalyst system and the scale-up technology. And PLA was melt blended with polypropylene (PP) and elastomer, glass fiber with the various ratio of PLA/PP/elastomer/glass fiber, L-PLA/ D-PLA / elastomer /glass fiber in the twin screw extruder. The mechanical and thermal properties of such as tesile, flexural and impact were studied. It was found that new PP/PLA elastomer/glass fiber composites and strereo-complexed PLA composites could be applied to auto parts applications.