Abstract: In order to further evaluate the clinical efficacy and safety of seaweed polysaccharide soluble powder as a feed additive in large-scale application in swine production,a total of 150 naturally porcine circovirus type 2(PCV2)infected pigs 35 to 50 days of age were randomly divided into 3 groups with 50 pigs in each group.The tested drug group fed the diet with supplementation of 200 mg/kg seaweed polysaccharide soluble powder for 7 consecutive days.The drug control group whose diet was added with 200 mg/kg Astragalus polysaccharide powder for 7 consecutive days.The positive control group received no dietary addition treatment.Ten random serum samples from each group were collected on one day before treatment as well as the 7^th and 14^th day post treatment,respectively,and the serum levels of IL-2,IL-6,INF-γ,TNF-α and IgG were determined.The results showed the dietary supplementation of 200 mg/kg seaweed polysaccharide soluble powder elevated the serum levels of IL-2,IL-6,TNF-α,INF-γ and IgG in pigs with natural PCV2 infection;during the experimental period,no adverse reactions were observed in the swine fed with diet adding 200 mg/kg seaweed polysaccharide soluble powder for 7 consecutive days.The combined data suggest that seaweed polysaccharide soluble powder enhances the immune function of pig and is safe for clinical use.