--- - |2+ Folate supplementation is recommended before and during early pregnancy to prevent neural tube defects, but the effect of red blood cell (RBC) folate on large for gestational age (LGA) is still unknown. We performed a nested case‐control study including 542 LGA cases and 1,084 appropriate for gestational age (AGA) controls to examine the association of RBC folate concentrations with risk of LGA. Then, male offspring of dams fed basic folic acid (2 mg/kg, control) or 10‐fold folic acid (20 mg/kg, HFol) diet before and during pregnancy were used to explore the effect of high folate intake on birth weight and long‐term effects. We observed higher RBC folate concentrations in the cases compared to controls (p = 0.039). After adjustment for maternal age, BMI at enrollment, gestational weeks at enrollment, gestational weeks at delivery and infant gender, higher RBC folate levels were significantly associated with increased risk of LGA (Ptrend = 0.003). Interestingly, male offspring of HFol dams showed the higher birth weight, elevated levels of post loading blood glucose at 9 and 13 weeks post‐weaning and increased triglyceride (TG) and total cholesterol (TC) levels at 17 weeks post‐weaning. Furthermore, we observed that high folate intake increased the proliferation and differentiation of adipose cells. Our results suggest that maternal high folate intake confers the risk of LGA birth and accelerates the development of obesity in male offspring. - Journal of Cellular Physiology, Volume 233, Issue 12, Page 9383-9389, December 2018.