Abstract: By supplementing low protein diets with amino acids,the effects on the growth performance and blood biochemical indicators on growing pigs were evaluated.Fifty four crossbred growing pigs(Duroc譒andrace譒arge White)with an average body weight of 18.0?0.5 kg were randomly assigned to 3 treatment groups(3 duplicates,6 pigs per duplicate)by a randomized complete block design.The feed formulation included 18.59% crude protein and 0.85% apparent digestible lysine for the control group,in accordance with NRC(1998)standards.These levels also represent the current feed nutrition at large-scale pig-breeding farms in Fujian.The protein content was reduced to16.96% for Treatment I and 15.53% for Treatment II.The dietary lysine was kept constant for all treatments by supplementing each group with synthetic lysine,and with synthetic methionine and threonine according to the ideal model.As compared to the control group,the average daily weight gain increased 3.83% for Treatment I,and 2.59% for Treatment II(P0.05);FCR improved by 3.54%(P0.05)in Treatment I,while decreased by 1.18% in Treatment II(P0.05);and,the serum urea nitrogen decreased by 10.43% in Treatment I(P0.05)and 26.78% in Treatment II(P0.01).No significant difference among treatments was found on total protein and albumin in serum(P0.05).Growth performance and relative blood biochemistry of the pigs were improved with decreasing(i.e.,1.5% and 3%)dietary protein intake.