A 2×5 factorial experiment containing two ME and CP levels (12.12 MJ/kg and 20%, 10.91 MJ/kg and 18%) and five lysine levels (0.65%, 0.80%, 0.95%, 1.10% and 1.25%) was conducted to evaluate the effects of dietary energy and protein levels on lysine requirement of Beijing ducks from 7 to 21 days of age. Five hundred and sixty 7-day-old male Beijing ducks were randomly divided into 10 groups with 8 replicates in each group and 7 ducks in each replicate. These Beijing ducks were raised with experimental diets from 7 to 21 days of age. The results showed that: compared with ducks fed low ME and low CP diet, daily feed intake, feed/gain and lysine daily intake of ducklings fed high ME and high CP diet were reduced significantly (P＜0.05), but feed/gain, energy and protein daily intake had no significant difference (P>0.05) Daily weight gain, feed/gain and lysine daily intake were affected significantly by dietary lysine level. The lysine requirements of Beijing ducks from 7 to 21 days of age for optimal feed/gain at high and low ME, CP levels which were estimated by brokenline regression analysis were 0.90% and 0.80% of diet, respectively. However, when lysine requirement was expressed as a percentage of CP, the lysine requirements for optimal feed/gain at high and low ME, CP levels were 4.50% and 4.44%, respectively. It was concluded that lysine requirement should be expressed as a percentage of dietary CP when dietary energy and protein levels were changed.