This experiment was conducted to study the effects of dietary protein levels on growth performance, serum biochemical indices and nitrogen metabolism of silver foxes. Sixty male silver foxes aged 9 weeks with a similar body weight were randomly divided into 5 groups with 12 replicates per group and 1 fox per replicate, and they were fed diets containing 37.83%, 35.54%, 33.22%, 30.10% and 22.70% protein, respectively. The pre-trail period lasted for 12 d, and the trial period lasted for 45 d. Changes of body weight and feed intake were recorded; digestion and metabolism trials were carried out from the 25th to 27th day of the trial period, and samples of feed, fecal and urine were collected to determine nitrogen content; on the 31st day, blood sample was collected for analysis of serum albumin content, alkaline phosphatase activity, as well as concentrations of urea nitrogen and total cholesterol. The results showed as follows: 1) dietary protein levels had significant effects on body weight and average daily gain (P<0.05); the body weight on the 31st day and the final of foxes fed diet with protein level of 37.83% was significantly higher than that of foxes fed diet with 22.70% protein (P<0.05). 2) Dietary protein levels had significant effects on serum urea nitrogen concentration and alkaline phosphatase activity (P<0.05); with the decrease of dietary protein level, serum alkaline phosphatase activity tended to decrease at first and then increase, while serum urea nitrogen concentration acted as an opposite tend. 3) Dietary protein levels had significant effects on nitrogen intake, urea nitrogen, nitrogen apparent digestibility, nitrogen retention and nitrogen retention ration (P<0.05); nitrogen apparent digestibility, nitrogen retention and nitrogen retention ration levels tended to decline with dietary protein level decreased; there were no significant differences in nitrogen excretion among groups (P>0.05), the values of nitrogen excretion in 22.70% and 33.22% protein groups were lower, and that in 37.83% protein group was the highest. These results indicate that dietary protein levels can be reduced to 30.10% from 37.83% without negative effects on growth performance of foxe, and the 33.22% is considered to be an optimal protein level with lower environmental pollution and maintained growth performance.