Abstract: In the study, molecular mass distribution of Astragalus Polysaccharides (APS) was investigated by ethanolprecipitation (step and stepwise) and ultrafiltration. The results indicated: For step ethanol precipitation, yields of APS wereincreased with the increase of ethanol concentration. There were high differences in the saccharides content of samples, the lowcontent was observed when using 60% ethanol, but, high contents were obtained using 30% and 70% respectively. For stepwiseethanol precipitation, APS ratio was highest at ethanol concentration of 10%, while most APS might be precipitated whenethanol concentration was up to 80%. APS content was very low when using 90% ethanol, and the rest contents were notapparently different under ethanol concentrations ranging from 10% to 80%. After ultrafiltration, most APS (57.6%) weredistributed in the centrifuged pellets of more than 150kDa fraction. There was not much difference in the saccharides contentsexcept for those of less than 3kDa and 6～50kDa fractions. Both high and low molecular masses of APS were of highpolysaccharides, however the saccharide content of 3～150kDa APS was only 13.2%. Therefore, molecular mass distributionwas very uneven in APS.

Key words: Astragalus polysaccharides, ethanol precipitation, ultrafiltration, molecular mass distribution