The aim of the paper is to investigate the technics of isolating the immune-active polysaccharides from Herba Spirodelae seu Lemnae(PHS) by ultrafiltration.PHS were extracted and isolated through decoction,ultrafiltration,(removal) of protein and ethanol precipitation et al.The total contents of saccharides in the extraction and sample were(determined) by the methods of sulphuric acid phenol and sulphuric acid anthrone.The protein contents were determined by colorimetric method of coomassie brilliant blue G 250.Some hazel powder was gained.The purity,the contents of protein,and the recovery are 53.5%,1.2%,and 6.43%,respectively.Ultrafiltraion is a kind of method,which can isolate PHS simply,quickly and effectively.