The objective of this study was to determine the protein requirements of female mule ducks during the starting (0 to 3 wk), growing (4 to 7 wk), and finishing (8 to 10 wk) periods. We performed 1 trial for each period. Five increasing dietary protein levels were tested for each period. All diets had the same ME content (12.12 MJ of ME/kg of feed), and the ratios between the main amino acids and lysine and the lysine-to-protein levels were similar. Six pens of 22 or 25 ducks were used per treatment. By adjustment with the more accurate model, the evolution of average BW, FCR, and weights of breast muscle and thighs with shanks was evaluated according to the protein level in the diets for each period. On the basis of our findings, 23.5, 15.4, and 13.8% CP levels could represent optimal levels in the starting, growing, and finishing diets, respectively. Increasing the protein level in diets for the starting, growing, and finishing periods from 15.4 to 25.3%, 10.8 to 16.6%, and 10.2 to 18.0%, respectively, decreased the efficiency of body protein deposition from 54 to 42%, 47 to 42%, and 79 to 45%, respectively. As a consequence, the nitrogen content in feces increased by 1.5-, 2.0-, and 1.9-fold, following a linear relationship with dietary nitrogen content