The effect of dietary N-carbamylglutamate (NCG) supplementation during the entire gestation on reproductive performance of gilts was determined. At the initial day of gestation, forty-five cross-bred (Landrace × Large white) gilts were randomly assigned to five groups receiving a basal diet (control group) and basal diet supplemented with 0.05%, 0.10%, 0.15% and 0.20% NCG until parturition, respectively. At parturition, total litter size, live litter size and rate of stillbirth were not markedly affected by NCG supplementation. However, gilts in 0.05% NCG-supplemented group had more pigs born alive than gilts in control group (+1.11 pigs, p = 0.12), and live litter weight was increased (+12.13–19.17%, p < 0.05) in 0.05%, 0.10% and 0.15% NCG-supplemented groups relative to control group. And also, average birthweight of piglets born alive was higher (+6.57%, p < 0.05) in 0.05% NCG-supplemented group than in control group. Furthermore, on days 30, 60, 90 and 110 of gestation, concentrations of arginine and ornithine in plasma were higher (p < 0.05) in 0.05%, 0.10%, 0.15% and 0.20% NCG-supplemented groups than in control group, respectively. In addition, the chorioallantois gene expression of endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor A (VEGF-A), placental growth factor (PLGF) and angiopoietin-2 (ANG-2) was all increased (p < 0.05) in 0.05%, 0.10% and 0.15% NCG-supplemented groups than in control group. In conclusion, dietary supplementation with 500 mg/kg NCG during the entire gestation significantly improves pregnancy outcomes in gilts, which may be associated with the improved concentrations of arginine in plasma and placental angiogenic factors gene expression of gilts.