PLA polymer films with different thickness (2mm, 50μm, and 25 μm) and crystallinity (amorphous and semi-crystalline) were degraded in water and moisture (RH) environments to understand the role of physical structures and environmental parameters in the degradation process of lactic acid based polymers. The degradation studies were conducted in water and moisture environment maintained at 60 and 80°C. Various analytical techniques were applied to monitor the changes in the rate/or mechanism of degradation. Weight loss, pH value, titration, and molecular weights and molecular weight distributions were measured to evaluate the extent of degradation. Size exclusion high performance liquid chromatography (SEC-HPLC) was used as a quantitative tool to analyze the products from the degradation. The results showed that the rate of degradation high at the beginning (first few days) decrease significantly over time. Also, the results suggest a dominant contribution by the end groups and hydrolysis of ester linkage as the primary mechanism of degradation of PLA. Spatial variations and gradient in rate of degradation of PLA matrix was also investigated. On the basis of these data, a probable route of PLA degradation has been suggested.