OBJECTIVE: Recent research has shown that brain-derived neurotrophic factor (BDNF) can improve obesity. This study aimed to explore the relationship between BDNF and birth weight by measuring BDNF levels in the umbilical cord blood of neonates. METHODS: Based on birth weight, 51 first-born full-term healthy neonates were classified into 3 groups: small for gestational age (SGA, n=8), appropriate for gestational age (AGA, n=31) and large for gestational age (LGA, n=12). Height and birth weight as well as umbilical concentrations of BDNF, leptin, insulin, total cholesterol and triglyceride were determined. RESULTS: BDNF level in the SGA group (19 980.00±5 470.54 pg/mL) was significantly higher than that in the AGA (10 598.00±6 295.71 pg/mL) and LGA (7 508.57±3 767.81 pg/mL) groups (P<0.05). There was no significant difference in the BDNF level between the AGA and LGA groups. Stepwise regression analysis showed that the value of BDNF was negatively correlated with birth weight and BMI of neonates, but had no correlation with leptin and insulin levels. Leptin levels showed positive correlations with birth weight and BMI of neonates. There were no significant differences in total cholesterol and triglyceride levels among the three groups. CONCLUSIONS: BDNF is closely correlated to birth weight but not correlated with leptin and insulin in neonates.