The experiment was conducted to study the effects of dietary different protein levels with supplementation of compound amino acid on performance and the N excretion of lactating sows in summer. One hundred and twenty Large White×Landrace multiparous sows were randomly divided into 3 groups based on the concentration of crude protein (19.5%, 18.5% and 17.5%), each group containing 40 replicates with 1 sow per replicate. Three diets were all supplemented with compound amino acid including Lys, Val, Thr, Met and Trp. The sows were fed until piglets weanling. The results showed as follows: 1) litter weanling weight and litter gain in 18.5% group were significantly higher than that in 17.5% group (P<0.05), and had no significant differences compared with 19.5% group (P>0.05); no significant differences were found in average daily feed intake, back fat losses and weanling-to-estrus interval of sows among 3 groups (P>0.05); 2) plasma urea nitrogen levels in 18.5% group were significantly lower than those in 17.5% group (P<0.05), and had no significant differences compared with 19.5% group (P>0.05); concentration of partial plasma amino acid in 18.5% group was lower than that in 17.5% group and 19.5% group (P<0.05), while concentration of partial milk amino acid in 18.5% group was higher than that in 17.5% group and 19.5% group (P<0.05); 3) no significant difference was found in apparent N digestibility among different groups (P>0.05); fecal N excretion decreased by 6.0% per 1% reduction of protein concentration. These results indicated that dietary 18.5% protein level with supplementation of compound amino acids could elevate the performance of sows in summer (average temperature=29.5 ℃).［Chinese Journal of Animal Nutrition, 2010，22（2）:285-292］