This experiment was conducted to assess the effects of dietary nitrogen and phosphorus levels on growth performance, carcass traits and serum biochemical indexes of broilers, and to provide reference for the recommended allowance of crude protein and phosphorus in diets of broilers. One thousand and two hundred 1-day-old healthy Ross 308 broilers were reared under four feeding phases system: 1 to 7 days of age, 8 to 21 days of age, 22 to 35 days of age and 36 to 40 days of age, and those in each feeding phase were randomly divided into 4 groups with 10 replicates per group and 30 birds per replicate, male and female half and half. The experimental diets were corn, wheat and soybean meal, and according to the dietary nitrogen and phosphorus levels, the four groups were higher-nitrogen-higher-phosphorus group [HH group, crude protein (CP): 22.70%, 21.60%, 19.50% and 17.50%; non-phytate phosphorus (NPP): 0.45%, 0.40%, 0.35% and 0.30%), higher-nitrogen-lower-phosphorus group (HL group, CP: 22.70%, 21.60%, 19.50% and 17.50%; NPP: 0.30%, 0.25%, 0.20% and 0.15%), lower-nitrogen-higher-phosphorus group (LH group, CP: 20.70%, 19.70%, 17.70% and 15.70%; NPP: 0.45%, 0.40%, 0.35% and 0.30%) and lower-nitrogen-lower- phosphorus group (LL group, CP: 20.70%, 19.70%, 17.70% and 15.70%; NPP: 0.30%, 0.25%, 0.20% and 0.15%), and HL group and LL group were supplemented with 500, 1 000, 1 500 and 2 000 U/kg thermostable phytase (TP), respectively. The results showed as follows:1) at 1 to 35 days of age, the 35-day-old average body weight (ABW) of HH group and HL group was significantly higher than that of LH group (P<0.01) and LL group (P<0.05). The average daily gain (ADG) of HH group and HL group was significantly higher than that of LH group (P<0.05). The feed to gain ratio (F/G) of HL group was significantly lower than that of LH group and LL group (P<0.05). The average daily feed intake (ADFI) of HH group was significantly higher than that of LH group (P<0.01) and LH group (P<0.05); at 1 to 40 days of age, the 40-day-old ABW of HH group was significantly higher than that of LH group (P<0.05). The ADG and ADFI of HH group were significantly higher than those of LH group (P<0.05). There was no significant difference in the other indexes among groups (P>0.05). 2) The activity of serum alkaline phosphatase of HH group and LH group was significantly higher than that of LL group (P<0.01) and HL group (P<0.05). The content of serum uric acid of HH group was significantly higher than that of LH group (P<0.01) and LL group (P<0.05), and that of HL group was significantly higher than that of LH group (P<0.05). There were no significant differences in the other serum biochemical indexes and carcass traits (P>0.05). The results indicate that, at 1 to 35 days of age, the HL group (CP: 22.70%, 21.60%, 19.50% and 17.50%; NPP: 0.30%, 0.25%, 0.20% and 0.15%; TP: 500, 1 000, 1 500 and 2 000 U/kg) for Ross 308 broilers obtains the best body weight gain and economical profit; at 1 to 40 days of age, the LL group (CP: 20.70%, 19.70%, 17.70% and 15.70%; NPP: 0.30%, 0.25%, 0.20% and 0.15%; TP: 500, 1 000, 1 500 and 2 000 U/kg) obtains the best economical and exobiology profit.