Abstract: Objective: To study the protective effects of polysaccharide from Polygonati rhizoma (PSP) on acute behavioral despair mice and the underlying mechanisms. Methods: A total of 60 ICR mice were randomly divided into the control group, the paroxetine group (10 mg/kg), PSP-low group (100 mg/kg), PSP-medium group (200 mg/kg), and PSP-high group (400 mg/kg). After 3 weeks of administration, the effect of PSP on the body weight and locomotor activity of mice was investigated by body weight and open field. The tail suspension and the forced swimming test were conducted to evaluate the antidepressant effect of PSP. In addition, 5-hydroxytryptamine (5-HT), norepinephrine (NE), dopamine (DA) levels in cortex, tumor necrosis factor (TNF-α), interleukin-10 (IL-10) levels in serum as well as tryptophan (TRP), 5-hydroxyindolacetic acid (5-HIAA) and 3-hydroxycaninuric acid (3-HK) contents in hippocampus of mice were evaluated to explore the molecular mechanism of antidepressant effect. Results: The PSP administration remarkably shortened the immobility time of the behavioral despair model mice both in tail suspension test and forced swimming test (P<0.05), showing the antidepressant activity. At the same time, PSP had no influence on the body weight and locomotor activity of mice (P>0.05). Moreover, PSP (200 and 400 mg/kg) significantly elevated the levels of 5-HT, DA and NE in cortex (P<0.05), decreased the TNF-α and IL-10 release in serum (P<0.05), as well as inhibited the levels of TRP and 3-HK (P<0.05) in hippocampus of mice compared to those of control group. Conclusion: PSP (200 and 400 mg/kg) exerted remarkable antidepressant activity in behavioral despair mice probably by promoting monoamine neurotransmitter release, inhibiting inflammatory cytokines levels, and regulating tryptophan metabolism.