To investigate the effects of l-Arginine in treating asymmetric fetal growth restriction (FGR).A total of 66 pregnant women whose fetuses were diagnosed with asymmetric fetal growth restriction were divided into two groups. Group 1 consisted of 36 women who were given routine therapy alone; group 2 consisted of 30 women who were given l-Arginine and routine therapy; and the control group consisted of 30 more women with a normal pregnancy.Before treatment, mean maternal serum levels of NO 2 − /NO 3 − were significantly lower in groups 1 and 2 than in the control group (P<0.01). After treatment, maternal serum levels of NO 2 − /NO 3 − were considerably higher in group 2 than in group 1 (P<0.01). Mean birth weight was significantly higher in group 2 than in group 1 (P<0.05), but still lower in group 2 than in the control group (P<0.01).A deficiency in nitric oxide may play an important role in the development of asymmetric fetal growth restriction. l-Arginine can be used to increase maternal NO 2 − /NO 3 − levels and newborn birth weight.