This experiment was conducted to research the effects of dietary protein level on growth performance, nitrogen metabolism, protease activities in intestine, serum biochemical indices and serum hormone indices of growing Rex rabbits. Two hundred weanling Rex rabbits with an average body weight of (620?30) g were randomly divided into 5 groups with 40 replicates in each group and each replicate contained 1 rabbit. Rabbits in the 5 groups were fed experimental diets containing 14.5%, 16.0%, 17.5%, 19.0% and 20.5% protein, respectively. The experiment included a pretrial period of 7 days and an experimental period of 53 days. The results showed as follows: dietary protein level had significant influence on average daily gain, average daily feed intake, feed/gain, nitrogen intake, nitrogen retention and digestible nitrogen (P<0.05 or P<0.01), but had no significant influence on fecal nitrogen, urine nitrogen, nitrogen apparent digestibility, nitrogen bioavailability and nitrogen utilization rate (P>0.05). Dietary protein level significantly affected serum globulin content (P<0.05), while did not significantly affect other serum biochemical indices, including the contents of total protein, albumin, cholesterol and urea nitrogen, and albumin/globulin (P>0.05). Otherwise, the activities of trypsinase and chymotrypsin in intestine, and levels of growth hormone, insulin and insulin-like growth factor-1 (IGF-1) in serum were not significantly affected by dietary protein level (P>0.05). The results indicate that dietary optimal protein level can improve average daily gain, average daily feed intake and nitrogen utilization rate, and reduced the feed/gain, but has little effects on intestinal protease activities and serum indices. Based on the feed/gain and nitrogen retention, the dietary optimal protein level estimated by nonlinear regression model are 18.51% and 19.45%, respectively.