To evaluate the effects of crude hedysari polysaccharide (CHPS) on growth performance, serum biochemical parameters and antioxidant capacity in weaner piglets challenged with lipopolysaccharide (LPS), thirty-two healthy weaner piglets were randomly allocated to control group (basal diet), LPS group (basal diet+LPS), CHPS low-dose group (basal diet+LPS+200 mg/kg CHPS), and CHPS high-dose group (basal diet+LPS+800 mg/kg CHPS), respectively. According to the records of daily feed intake by group and the body weights on days 1, 21 and 28, average daily gain (ADG), average daily feed intake (ADFI) and the ratio of feed to gain (F/G) were calculated. Piglets in the LPS group and CHPS groups were injected intraperitoneally with 100 μg/kg·BW LPS on day 21, while the piglets in the control group were injected with normal saline at the same dose. Serum samples were obtained for analysis serum biochemical parameters at 3 h post-injection. The experiment lasted for 28 days. The results showed as follows: 1) compared with the control group, LPS challenge (22 to 28 d) significantly decreased ADG and ADFI in LPS group (P<0.01), significantly increased the activities of serum alkaline phosphatase (AKP) and glutamic-pyruvic transaminase (GPT) and the contents of triglyceride (TG), total cholesterol (TC), urea nitrogen (UN) and malondialdehyde (MDA) in LPS group (P<0.05 or P<0.01), and significantly decreased nitric-oxide synthase (NOS) activity (P<0.05). 2) Compared with the LPS group, ADG and ADFI in CHPS groups were significantly increased (P<0.05), and the contents of serum TG, TC and MDA in CHPS low-dose group were significantly decreased (P<0.05 or P<0.01), and the activity of AKP in CHPS high-dose group was significantly decreased (P<0.01). These results indicate that the supplementation of CHPS in the basal diet inhibits the decrease of growth performance, decreases the contents of TG, TC and MDA and activity of AKP in the serum. CHPS can effectively relieve the immune stress of weaner piglets challenged with LPS.