A multi-angle laser light scattering (MALLS) method to determine molecular weight and its distribution of poly-Lactic Acid (PLA) was introduced and experimental procedure and results were given in the paper.This method took THF as solvent and mobile phase,and size exclusion chromatography (SEC) column as separation system combined with in-line MALLS and Refractive Index detector (RI).The molecular weight of the sample varied from 30000 to 150000 g/mol,and its distribution((?)) varied between 1.3 and 1.8.