This experiment was conducted to investigate the effects of dietary nicotinic acid supplemental level on meat quality, hair follicle development and immune performance of growing Rex rabbits. A total of 160 three-month-old Rex rabbits with similar body weight were randomly divided into 4 groups with 40 replicates per group and 1 rabbit per replicate. Rabbits in the control group were fed a basal diet, and the others in the experimental groups were fed the experimental diets supplemented with 3, 6 and 12 mg/kg riboflavin, respectively. The pre-test period lasted for 7 days, and the experimental period lasted for 53 days. The results showed that compared with the control group, dietary supplemented with 6 and 12 mg/kg riboflavin significantly reduced the meat drip loss of Rex rabbits (P<0.05), dietary supplemented with 3, 6 and 12 mg/kg riboflavin significantly increased the skin total hair follicles density of Rex rabbits (P<0.05), dietary supplemented with 3 and 6 mg/kg riboflavin significantly increased the skin primary hair follicles density of Rex rabbits (P<0.05), and dietary supplemented with 6 and 12 mg/kg riboflavin significantly increased the skin secondary hair follicles density of Rex rabbits (P<0.05), dietary supplemented with 6 and 12 mg/kg riboflavin significantly decreased the ratio of secondary hair follicles density to primary hair follicles density of Rex rabbits (P<0.05). Dietary riboflavin supplemental level significantly affected the thymus weight, thymus index and the content of immunoglobulin G, immunoglobulin A and interleukin 2 in serum of Rex rabbits (P<0.05), and all the above indices were showed a firstly increase then decrease tendency with dietary riboflavin supplemental level increasing, and got the max value in the 6 mg/kg supplemental group, which significantly higher than those in the control group (P<0.05). In conclusion,the suitable dietary riboflavin supplement level of growing Rex rabbits aged from 3 to 5 months is 6 mg/kg (measured dietary riboflavin level is 8.35 mg/kg).