An experiment was conducted to investigate the effect of dietary crude protein (CP) level on growth performance, carcass quality, serum biochemical parameters, immune indexes, nitrogen emission and nitrogen apparent availability in broilers, so as to estimate the minimum CP requirement of broilers fed corn-soybean diet from 22 to 42 days of age. A total of 360 22-day-old male broilers were randomly assigned to 5 groups with 10 replicates per group and 6 birds each replicate.The birds were fed the diet containing CP 19.87% (control), 18.84%, 17.63%, 16.81%, 15.75% or 14.88% for 21 days. The nitrogen metabolism test was conducted from 38 to 42 days of age. The results showed as follows:broilers fed lower CP level diets had significantly higher values of ratio of feed to gain, percentage of abdominal fat, drip loss and a^* values of breast meat, a^* and b^* values of thigh meat, serum contents of total cholesterol, triglyceride and uric acid, as well as nitrogen apparent availability (P<0.05). Average daily gain, L^* of breast meat, serum ND antibody titer and fecal nitrogen were significantly increased as the dietary CP level decreased, respectively (P<0.05). Compared with the control, no significant differences were observed in the above mentioned indexes for broilers fed diets containing 17.63% of CP (P>0.05), however, nitrogen content in feces was significantly lower (P<0.05). Broilers fed diets containing 16.81% or lower CP had significantly lower average daily gain and ND antibody titer (P<0.05). Ratio of feed intake to body gain, abdominal fat, drip loss of breast meat, serum total cholesterol and triglyceride were significantly higher when chicks were fed diets with lower CP than 16.81%, respectively (P<0.05). Therefore, the minimum dietary CP requirement of broilers from 22 to 42 days of age is suggested as 17.63%.