Abstract: Crossbred (Limousin × Lu-xi) beef cattles, fitted with permanent cannulas in the rumen, and catheter into jugular vein, were used in the study. The experiments were divided into three stages according to three dietary levels of NPN and sulfur (0％ and 0.150%，1％ and 0.225%，2％ and 0.300%), each level corresponded with three concentrations of copper that were 10, 25 and 50 mg/kg in the diets, and were conducted in Latin square designs to access the effects of dietary NPN and sulfur on metabolism of nutrients, the bioavailability and the requirement of copper in beef cattles. The results indicated that plasma copper concentration and activities of Cp or SOD increased (P<0 .05)，but the synthesis of ruminal MCP reduced with increasing dietary copper in the same level of NPN and sulfur in the diets. In the presence of high dietary NPN and S concentration, the bioavailability of dietary copper declined，but the synthesis of ruminal MCP increased (P< 0.05). It was suggested that the optimal requirements of copper were 10, 10 and 25 mg/kg for cattles fed diets containing urea and sulfur 0% and 0150%, 1% and 0.225%, 2% and 0.300% respectively.

Key words: cattle, NPN, sulfur, copper, requirement