The growth response, total hemocyte count (THC), respiratory burst (release of superoxide anion), phenoloxidase (PO) activity, superoxide dismutase (SOD) activity, nitric oxide synthase (NOS) activity as well as resistance to the pathogen Vibrio alginolyticus were measured in Litopenaeus vannamei, which had been fed diets supplemented with glycyrrhizin (the aqueous extract of licorice, Glycyrrhiza glabra, roots) at 0, 50, 100, 150, and 200 mg/kg of feed for 8 wk. In the feeding trial, there was no significant difference in survival rate (P >0.05). Significant higher specific growth rate was observed in treatments with dietary glycyrrhizin than that in the control group (P <0.05). Shrimp fed a diet with 200 mg/kg of glycyrrhizin had significant higher THC, PO activity, respiratory burst activity and SOD activity than that in the control group (P <0.05). Increased THC, respiratory burst activity and NOS activity were also noticed in shrimp fed glycyrrhizin at 100 or 150 mg/kg (P <0.05). There were significantly lower cumulative mortalities after the disease challenge in shrimp fed glycyrrhizin diets (8.33-16.67%) than that in the control group (36.67%) (P <0.05). These results indicated that glycyrrhizin may enhance the nonspecific immune system, increase the resistance of L. vannamei as well as improve production in shrimp farming.