Niacin is an essential nutrient for growth and health of fish. The signs of niacin deficiency in most fish species are loss of appetite, poor growth and increased mortality. The objective of this study is to detect the suitable requirement of niacin in diet of juvenile Ctenopharyngodon idellus, a primary aquacultural breed in China. Prior to the start of experiment, all the fish were acclimated to the experimental condition for 2 weeks and fed the basal diet，then thirty healthy fish were randomly distributed to each of 21 experimental fiberglass tanks connected to a flow through system. Niacin was added to the basal diet at 0, 10, 20, 40, 80, 160, 320mg•kg-1 diet, and the actual content of niacin in diets were 5.1, 9.8, 16.6, 32.2, 66.7, 130.1, 271.5mg•kg-1 diet respectively based on determination by High Performance Liquid Chromatography (HPLC). The 7 dietary were fed to randomly assigned triplicate groups of fish (initial body weight 12.43±1.80g). All fish were fed at a rate of 2-3% of their body weight per day in three equal feedings. Fish were batch-weighted by tank once every two weeks and the daily ration were adjusted accordingly. Experiment was conducted for 8 weeks. The results showed that: 1. The addition of niacin to diets had no effect on condition factor but significantly improved fish specific growth rate(SGR) ,weight gain rate(WGR) and survival rate(SR). The highest SGR and WGR were observed at group of 32.2 mg•kg-1, while feed conversion rate(FCR) were lowest，these indexes had significant difference from the other 6 groups; 2. There were no significant difference in carcase moisture, crude ash of the fish. The crude lipid of fish in experimental groups were significantly higher than the control group but there were no difference among the experimental groups. The crude protein of 66.7 mg•kg-1 group were significantly higher than the control group and 9.8mg•kg-1 group; 3. The addition of niacin to diets significantly improved hemoglobin(HB) and red blood count(RBC) but had no effect on serum cholesterol(CHOL) and triglyceride(TG). The high density lipoprotein cholesterol(HDL-C) and Low density lipoprotein cholesterol(LDL-C) were significantly higher than the control group and 9.8 mg•kg-1 group when the fish fed above 16.6 mg niacin per kg diet. The results of this study demonstrated that dietary niacin could improve growth performance, decrease mortality. Using the broken-line analysis model，the dietary niacin requirement for juvenile Ctenopharyngodon idellus based on specific growth rate(SGR) was 25.5mg•kg-1 which could maintain maximum growth of the fish.