The present study aimed to evaluate the mechanisms modulated by dietary arginine supplementation to sows during lactation regarding antioxidant capacity and vascularization of mammary glands. At 109 days of gestation, animals were transferred to individual farrowing crates equipped with manual feeders and automatic drinker bowls. Environmental temperature and humidity inside the farrowing rooms were registered every 15 min. At farrowing, sows were assigned in a completely randomized design to a control diet (CON) or the CON diet supplemented with 1.0% L-arginine (ARG). A total of three gilts and two sows were fed the CON diet, whereas three gilts and three sows were fed ARG diets. Sows were fed a fixed amount of 6.0 kg/day, subdivided equally in four delivery times (0700, 1000, 1300 and 1600 h) for 21 days. At weaning, sows were slaughtered and mammary tissue samples and blood from the pudendal vein were collected. Data were analyzed considering each sow as an experimental unit. Differences were considered at P<0.05. L-arginine fed sows presented lower messenger RNA (mRNA) expression for prolactin receptor (P=0.002), angiopoietin1 (P=0.03) and receptor tyrosine kinase (P=0.01); higher mRNA expression for prostaglandin synthase 1 (P=0.01); a trend of decrease for glucocorticoid receptor (P=0.06) and IGF receptor 1 (P=0.07); and a trend (P=0.05) for an increased glutathione peroxidase mRNA expression. The angiopoietin2:angiopoietin1 mRNA ratio tended to increase (P=0.07) in ARG fed sows. L-arginine fed sows had greater (P=0.04) volumetric proportion of blood vessels and a trend of enhance (P=0.07) in the number of blood vessels per mm2. These findings show that 1.0% ARG supplementation to sows activates proliferative mechanisms, may improve mammary tissues’ angiogenesis and tended to increase mRNA expression of genes that encode antioxidant enzymes in mammary gland of sows.