Abstract: A magnetic ultrafiltration membrane whose molecular weight cut-off (MWCO) can be between 31000 and 73000 under 0.2 MPa pressure and varying magnetic field intensity was prepared by in situ synthesis on the basis of a polysulfone ultrafiltration membrane with a MWCO of 80000 and used sequentially separate Angelica sinensis root polysaccharides with a purity of 97.5%. As a result, three fractions were obtained under various magnetic filed intensities and named as A, B and C, respectively. Their respective weight average molecular weights (Mw) were determined by high performance gel permeation chromatography (HPGPC) to be 86317, 19989 and 62461. Polysaccharides with a relative molecular weight ranging from 70000 to 100000 was 70% in fraction A. Roughly 95% of fraction B consisted of polysaccharides with a relative molecular weight between 10000 and 30000. Fraction C contained approximately 80% of polysaccharides whose molecular weight was in the range of 50000－70000.

Key words: polysaccharides from the root of Angelica sinensis, magnetic ultrafiltration membrane, high performance gel permeation chromatography (HPGPC), continuous separation