The experiment was conducted to estimate the effects of calcium and phosphorus levels on bone growth of broilers from 1 to 3 weeks of age. Eight hundred 1-day-old AA broilers with similar body weight were randomly allotted into 20 experimental treatments with 4 replicates of 10 broilers each. Broilers were fed diets with five levels of calcium (0.6%, 0.8%, 1.0%, 1.2% and 1.5%) and four levels of nonphytate phosphorus (0.35%, 0.45%, 0.55% and 0.65%) in a 5×4 factorial arrangement. The results showed as follows: dietary calcium and nonphytate phosphorus levels had significant effects on tibia ash, calcium and phosphorus contents in tibia (P<0.05). Tibia ash was significantly increased with the levels of calcium and nonphytate phosphorus increasing in diets. Dietary calcium and nonphytate phosphorus levels had significant effects on tibia strength (P<0.05). The tibia strength was increased quadratically while dietary calcium content was increased. The tibia strength was significantly increased (P<0.05) while dietary nonphytate phosphorus content was increased. Tibia strength was significantly decreased while dietary calcium levels were 1.5%, 0.6% and nonphytate phosphorus level was 0.35% (P<0.05). The results also suggested that the maximum tibia strength was obtained when calcium, nonphytate phosphorus levels were 1.0% and 0.65% during 1 to 3 weeks. The tibia ash and tibia strength prediction equation were as follows: Y1=13.384+22.873X1+53.237X2－7.747X12－14.505X1X2－37.070X22, Y2=－109.462+221.270X1+349.690X2－106.061X12+5.208X1X2－322.143X22; Y1 was tibia ash, Y2 was tibia strength, X1 was the dietary calcium level, and X2 was the nonphytate phosphorus level of diet. The results indicated that the requirements of calcium and nonphytate phosphorus for optimal tibia ash and tibia strength were 0.98%, 0.53% and 1.06%, 0.55%, respectively. ［Chinese Journal of Animal Nutrition, 2010，22（4）:1088-1095］