Effects of dietary valine (Val) supplementation on milk composition, average daily feed intake, back fat thickness, interval days from weanling to estrus of lactating sows, and growth performance of suckling pigs were investigated in this study. Thirty-two healthy sows (Landrace×Yorkshire, similar expected date of delivery, parity and body condition) were allocated into 4 groups with 8 replicates, each replicate containing 1 sow. Sows in control group, trial group 1, trial group 2 and trial group 3 were fed with basal diet (0.93% Lys, 0.84% Val) supplemented with 0, 0.10%, 0.25% and 0.40% Val, respectively. The experiment was from day 107 of gestation to day 21 of lactation (weanling). The results showed that, milk fat, milk protein, total solids, and solids-not-fat on day 1 and day 14 of lactation significantly increased with Val supplementation (P＜0.01), while lactose significantly decreased (P＜0.01), there were the best results in trial group 2 among all groups; weanling weight of litter and weanling gain weight of litter increased with dietary Val supplementation, and the two indices in trial group 2 increased by 14.92%(P＜0.05) and 22.17%(P＜0.05) compared with control group, and there were the best results in trial group 2 among all groups; Val supplementation had no significant effects on average daily feed intake of sows from day 1 to day 5, day 6 to day 10, day 11 to day 15, day 16 to day 21 and day 1 to day 21 of lactation, back fat thickness from day 1 of lactation to weanling, and interval days from weanling to estrus (P＞0.05). Therefore, dietary Val supplementation improved lactating performance of sows so as to get a better growth performance of suckling piglets. In this study, dietary Val content was 1.09% to maximize weanling weight of litter and weanling gain weight of litter.［Chinese Journal of Animal Nutrition, ２００9，２1（5）:727-733］