Abstract: The effects of radix astragali and acid-stress on contents of serum complement C3 and C4 in juvenile soft-shelled turtles (Pelodiscus sinensis) were researched.Both control and experimental groups were designed,and the diet of experimental groups was added 5% raw material powder of radix astragali.After feeding 4 weeks,the half of the soft-shelled turtles were sampled,and the others were also did after 24 h under acid stress condition.The contents of serum complement C3 and C4 were determined.Results demonstrated that the radix astragali significantly improved the production of complement C3 and C4,and the acid stress significantly decreased the content of complement C3 and C4,while the radix astragali had protective effects on this decreasing.The results suggested that the radix astragali had the ability of against acid stress.