Leptin is a satiety hormone secreted from the adipose tissue and human placenta. We previously demonstrated that severe preeclampsia up-regulated leptin mRNA expression in the placenta and elevated maternal plasma leptin concentrations. Preeclampsia is frequently related to generation of small for gestational age (SGA) infant especially in cases with severe preeclampsia. However, it is still controversial whether the increase in maternal plasma leptin levels is associated with fetal growth restriction without complication of preeclampsia. Therefore, the aim of the present study was to explore the relationship between maternal plasma leptin levels and fetal growth in non-preeclamptic (n = 98) and preeclamptic (n = 40) women. In non-preeclamptic pregnant women, plasma leptin levels in SGA group (n = 11) were significantly higher than those in appropriate for gestational age (AGA) group (n = 87, P<0.05). In pregnant women with preeclampsia, likewise, plasma leptin levels in SGA group (n = 15) were significantly higher than those in AGA group (n = 25, P<0.05). In multiple linear regression analysis, maternal BMI, mean arterial blood pressure and Delta SD of neonatal body weight were significant factors for determining maternal plasma leptin levels in all population studied. Maternal BMI and Delta SD of neonatal body weight showed positive correlation with maternal plasma leptin levels when analysis was performed in non-preeclamptic subjects alone. In conclusion, maternal plasma leptin levels reflect, at least partly, deterioration in fetal growth.