Growth assays were conducted to determine the dietary arginine and lysine requirements of mule ducklings. The metabolizable energy content of the basal diets used for the arginine and lysine requirement studies was 2810 and 2828 kcal/kg, respectively. Two-day-old ducklings of mixed sexes were fed on a starter diet for one week, fasted for 8 to 12 hr and then were fed on experimental diets for 12 or 14 days. Weight gain and feed consumption were recorded at the end of each experiment. The minimum requirements for arginine and lysine were obtained by regression analysis of weight gain or feed efficiency against arginine or lysine content in the diet. The minimum arginine requirements for maximum growth and efficiency of feed utilization were 1.08% of the diet or 6.0% of the dietary crude protein. The minimum requirements of the total lysine and available lysine were 1.06% and .97%, respectively, of the diet or 5.9% and 5.4%, respectively, of the dietary crude protein for both maximum growth and feed efficiency.