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The effect of microorganisms on degradation of PLLA was compared by using different kind of fungus in vitro. Fusarium L023 showed the strongest activity in accelerating the degradation of PLLA. Therefore, the in vitro degradation of PLGA copolymers was examined by immersing PLGA(50/50) and PLGA(70/30) films in media with or without Fusarium L023. Degradation of the polymeric films was monitored by measuring inherent viscosity and weight loss, as well as using techniques such as GPC, 1H NMR, DSC and SEM. In this case, the degradation of PLGA copolymers could be markedly accelerated by Fusarium L023. The microorganism assimilated the released oligomers as carbon-source, and this could explain why the inherent viscosity decreased more slowly for inoculated samples at the later stage than those in the controlled medium. Moreover, the Fusarium L023 would favor the degradation of PLGA copolymers by destroying the crystallization of PLLA segments at the later stage, which was caused by the preferential loss of glycotyl unit in the case of hydrolysis, for Fusarium L023 was more effective on accelerating the degradation of PLLA than PGA.