This experiment was conducted to investigate the effects of dietary copper supplemental level on growth performance, serum biochemical indices, fur quality and nitrogen metabolism of 3 to 4-month-old growing Rex rabbits. One hundred and sixty 3-month old healthy Rex Rabbits with similar body weight were randomly assigned to 4 groups with 40 replicates in each group and each replicate contained 1 rabbit. Rabbits in 4 groups were fed experimental diets which supplemented with 0, 30, 60 and 120 mg/kg copper (in the form of copper sulfate pentahydrate) based on a basal diet, respectively. The pre-experimental period lasted for 7 days and the formal test for 29 days. The results showed as followed:under the premise that there was no significant difference in initial body weight (IBW) (P>0.05), dietary copper supplemental level had significant influence on average daily gain (ADG) (P<0.05), and had extremely significant influence on average daily feed intake (ADFI). The ADG in adding 60 mg/kg copper group was significantly higher than that in no adding copper group and adding 120 mg/kg copper group (P<0.05). The ADFI in adding 60 and 120 mg/kg copper groups was extremely significantly higher than that in no adding copper group and adding 30 mg/kg copper group (P<0.01). Dietary copper supplemental level had significant influence on serum total protein content (P<0.05), and had extremely significant influence on serum albumin content (P<0.01). With the dietary copper supplemental level increasing, serum total protein and albumin contents were firstly increased and then decreased, and the highest values of them were all found in adding 30 mg/kg copper group. Dietary copper supplemental level had no significant influences on fur weight, fur thickness, fur area and hair length (P>0.05). Dietary copper supplemental level had extremely significant influences on intake nitrogen (IN), urinary nitrogen (UN) and nitrogen biological value (NBV) (P<0.01). When copper supplemental level was 30 mg/kg, the urinary nitrogen was the lowest and the nitrogen biological value was the highest. Considering all indexes of this experiment, the appropriate dietary copper supplemental level is 30 mg/kg for 3 to 4-month-old growing Rex rabbits (the measured value of diet copper content is 39.1 mg/kg).