The experiment was conducted to study the effects of yeast nucleotide on growth performance, body composition and serum immune indices of common carp （Cyprinus carpio）. Six hundred healthy common carp ［average body weight of （1.09±0.07） g and average body length of （3.60±0.34） cm］ were randomly allotted to 6 groups and each group included 3 replicates with 30 fish. Fish in 6 groups were fed with basal diet supplemented with 0 (control group), 258, 516, 774, 1 032, and 1 290 mg/kg yeast nucleotide (effective components), respectively. The trial lasted for 50 days. The results showed as follows: compared with the control group, the weight gain ratio (WGR), specific growth ratio (SGR) and protein efficiency ratio (PER) of yeast nucleotide supplementation groups were significantly increased （P<0.05）, at the same time, the feed conversion ratio (FCR）of yeast nucleotide supplementation groups was significantly decreased （P<0.05）. The highest WGR, SGR and PER (372.03%, 3.10%/d and 195.74%, respectively) and the lowest FCR (1.42) of fish were found in 516 mg/kg group, and the differences were significant between 516 mg/kg group and the other groups （P<0.05）. Based on broken-line model analysis of the WGR, SGR, PER and FCR, the optimal dietary yeast nucleotide supplemental levels for this formulation were 519.85 to 535.54 mg/kg. Body composition analysis showed that the crude ash and moisture contents in whole body were not affected by the supplementation of yeast nucleotide (P>0.05), but the crude protein and crude lipid contents were significantly higher with the increase of dietary yeast nucleotide supplemental level (516 to 1 290 mg/kg) than the control diet （P<0.05）. Compared with the control group, the activities of serum lysozyme (LSZ), superoxide dismutase (SOD) and catalase (CAT) of yeast nucleotide supplementation groups were significantly increased （P<0.05）, and the activities of these enzymes were increased first and decreased afterwards with the dietary yeast nucleotide supplemental level increasing. Fish had higher activities of serum LSZ and SOD when the dietary yeast nucleotide supplemental levels were 774 to 1 290 mg/kg, at the same time, the fish had a higher serum CAT activity when fed 516 to 1 032 mg/kg yeast nucleotide supplemental diets. Based on the above information, the optimal dietary yeast nucleotide supplemental levels in common carp diets for optimum growth performance and immune ability are 519.85 to 774.00 mg/kg.［Chinese Journal of Animal Nutrition，2011，23（1）：171-178］