This study investigated the effects of dietary arginine (Arg) supplementation, just during lactation, on sow and litter performance, plasma concentrations of metabolites and hormones, and milk yield and composition in multiparous sows. Thirty-one sows were randomly assigned to 3 dietary treatments supplemented with 0.0 (control, n=10), 0.5% (n=10), or 1.0% (n=11) L-Arg-HCl, respectively. Experimental diets were provided to the sows from d 3 to 21 of lactation. Plasma and milk samples were collected at d 14 and 21 of lactation. The average daily gain (ADG) of piglets from sows fed diets supplemented with 0.5 or 1.0% L-Arg-HCl at d 3 to 14 of lactation, were higher than that of controls (P<0.05). Maternal supplementation with 1.0% L-Arg-HCl also increased ADG of piglets between d 3 and 21 of lactation than that of the controls (P<0.05). There was no significant effect of supplementation on average daily feed intake (ADFI), body weight loss, and backfat thickness loss of lactating sows. Supplementation with 0.5 or 1.0% L-Arg-HCl had a trend towards increasing milk yields and milk fat contents (0.05