This study was conducted to determine the effect of black seed (B.S.) feeding (2.5%) and its residual effect on chemistry of ducklings serum. The obtained results reveal a significant decrease in the concentrations of all amino acids except histidine which showed a significant increase in ducklings
supplemented with (B.S.). On the other hand, stopping of B.S. supplemetation resulted in re-elevation of some amino acids such as glutamic acid, glycine, alanine, phenylalanine, lysine and arginine to the normal values after 12 days, while it significantly increased the values of cystine, tyrosine, valine, methionine, isoleucine, and histidine. The remainder amino acids still decreased. The activities of serum amino transferases Aspartate amino transferase (ASAT) and Alanine amino transferase (ALAT)). Alkaline and acid phosphatases, and creatinine values were not greatly affected, while the serum uric acid was significantly decreased in ducklings fed black seed.