To study the effects of compound non-starch polysaccharide (NSP) enzyme on the true metabolic rates of amino acids of cereals and their by-products, a complete randomized design and five metabolic test periods had been taken, and 56 healthy adult ducks with body weight of (2.0±0.2) kg were randomly divided into 7 groups with 8 replicates in each group and 1 duck in each replicate. The diets were single raw material+compound NSP enzyme. The true metabolic rates of amino acids of cereals and their by-products were detected before and after enzyme added. Results showed that after adding enzymes, some true metabolic rates of amino acids of wheat, corn, wheat bran, corn sugar residue and dried distillers' grains and solubles (DDGS) were significantly increased (P<0.05). And the range of amino acid effective nutrient improvement value (ENIV) of 14 kinds of ingredients was 0.01 to 1.24 g/kg, and the highest average ENIV were DDGS, corn sugar residue and wheat, and the average ENIV were 0.43, 0.30 and 0.23 g/kg, respectively. The lowest average ENIV was oat bran, and the average ENIV was 0.07 g/kg. Generally speaking, compound NSP enzyme can improve the true metabolic rates of amino acids and nutritive value of cereals and their by-products.