A 5-week feeding trial was conducted to study the effects of dietary nucleotides on non-specific immune and antioxidant indices of juvenile Litopenaeus vannamei. A total of 960 shrimp with an average body weight of (0.43±0.01) g were randomly allocated into 8 groups with 3 replicates per group and 60 shrimp per replicate. The control group were fed with the basal diet, while the other 7 groups were fed with the basal diets added with 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 g/kg the nucleotide mixture of adenosine-5′-monophosphate (AMP), cytidine-5′-monophosphate (CMP), uridine-5′-monophosphate (UMP) disodium salt, inosine-5′-monophosphate (IMP) disodium salt and guanosine-5′-monophosphate (GMP) disodium salt (1∶1∶1∶1∶1, m/m), respectively. The results showed as follows: shrimp fed diets with 0.4 to 1.2 g/kg nucleotide mixture had a significantly higher total haemocyte count (THC) (P<0.05 or P<0.01). Compared with the control group, serum superoxide dismutase (SOD) activity of 0.6 and 0.8 g/kg groups were significantly increased (P<0.05). The total antioxidation capacity (T-AOC) of 0.4 g/kg group was increased by 51.0% compared with the control group (P>0.05) and significantly higher than that of 1.2 g/kg group (P<0.05). With the increasing of dietary nucleotide mixture level, SOD activity and T-AOC in hepatopancreas of all groups increased at first and then decreased, and reached the highest value at 0.4 g/kg group. The activities of peroxidase (POD) and alkaline phosphatase (AKP) in serum and hepatopancreas were not significantly affected by nucleotide mixture supplementation (P>0.05). The anti-superoxide anion radical (O-2·) in 0.2, 0.4 and 0.6 g/kg groups was significantly higher than that of 1.0 and 1.2 g/kg groups (P<0.05), and there were no significant differences among the other groups (P>0.05). It is concluded that nucleotide mixture can improve the non-specific immunity and antioxidant capacity of juvenile Litopenaeus vannamei, and the optimal level of dietary nucleotide mixture for juvenile Litopenaeus vannamei is 0.4 to 0.6 g/kg.［Chinese Journal of Animal Nutrition, 2011, 23（5）：828 -835］
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