INTRODUCTION Lysine is the second limiting amino acid in poultry diets and the level of this amino acid is usually considered in diet formulation for ducks, but there is little research on the lysine requirements of early starter Pekin ducklings. The lysine requirement of NRC (1994) for Pekin ducklings from hatch to 14 days of age is 0.9%, but this recommendation is based on very few studies and only one study has been conducted before 21 days of age (Chen and Shen, 1979). Since the publication of the NRC (1994) recommendations, there have been few studies on the lysine requirement of starter Pekin ducklings. Bons et al. (2002) found that the lysine requirement for weight gain and gain/feed of male Pekin ducklings from hatch to 21 days of age was 1.17 and 1.06%, respectively, and Wang et al. (2006) estimated the dietary lysine need of White Pekin ducklings from hatch to 14 days of age to be 1.10% for weight gain. These data indicate that the lysine requirement of the modern starter Pekin ducklings may be higher than the NRC (1994) recommendation. However, to date, growth performance has served as the sole criterion for the determination of duck lysine requirements during the starter period and no consideration has been given to breast meat yield during this period. As the most valuable part of the poultry carcass, breast meat is more sensitive to dietary lysine deficiency than other skeletal meats in chicks (Tesseraud et al., 1996) and it was usually used to evaluate the effects of lysine on carcass characteristics of growing or finishing broilers (Moran and Bilgili, 1990; Acar et al., 1991; Bilgili et al., 1992; Kerr et al., 1999; Corzo et al., 2006; Tang et al., 2007; Dozier et al., 2008). However, a high dietary lysine level could also improve breast meat yield during the starter period, as confirmed by many studies in starter chicks (Tesseraud et al., 1999; Labadan et al., 2001; Urdaneta-Rincon and Leeson, 2004; Bastianelli et al., 2007) which suggested that breast meat yield could serve as another sensitive response criterion for evaluating the lysine requirement of poultry during the starter period. At present, Adams et al. (1983) and Bons et al. (2002) found improvements in breast meat yield of growing Pekin ducks fed diets with increasing lysine levels but no studies are available for starter ducklings. Therefore, the objective of our study was to determine the lysine requirements of modern White Pekin ducklings from 7 to 21 days of age based on growth performance and breast meat yield using graded dietary lysine levels.