Abstract: Bei Sha Shen, the roots of Glehnia littoralis, is a traditional Chinese medicinal herb commonly used as a drug nourishing Yin in Fu Zheng therapy. Our experiments showed that polysaccharides (GLP) isolated from Bei Sha Shen exhibited immunosuppressive activities.Intraperitoneal injection of GLP 48 h before antigen stimulation suppressed mouse-spleen PFC response to SRBC. The suppressive rate rose at first rapidly then slowly with incresing doses of GLP from 5 mg/kg to 800 mg/kg. It was found that the suppressive effect of GLP was reduced when it was given after antigen stimulation.The production of mouse serum hemagglutinin against SRBC was reduced by GLP when given ip 24 h before antigen stimulation with doses from 100 mg/kg to 1,000 mg/kg.A suppressive effect of GLP given ip with a dose of 500 mg/kg on mouse delayed hypersensitivity skin reaction induced by DNCB was observed. Experiments also showed that GLP could reduce the in vitro proliferation of human blood lymphocytes induced by PHA, Con A ad PWM.No effect on mouse spleen weight was found after the administration of GLP ip 800 mg/kg/d to mice for 7 days. LD₅₀ of GLP was more than 2,000 mg/kg when given ip to mice.This study indicates that GLP is a potent immunosuppressive agent which might be used in some diseases as an immunomodulator.