Objective To evaluate the effects of folic acid supplement on subjects with different 5, 10-methylenetet-rahydrofolate reductase (MTHFR) genotypes. Methods One hundred and eleven healthy women were divided into CC, CT and TT groups according to their MTHFR C677T genotypes. In each group subjects were randomly sub-divided into interven-tion (400 μg/d folic acid supplement) and control (usual diet) groups. The plasma folate, red blood cell (RBC) folate and plasma homocysteine (Hcy) concentration were measured at baseline and two months after intervention. Results The plasma folate was lower and the plasma Hcy was higher in the TT genotype than those in CC or CT genotypes (P＜0.05 or P＜0.01). After two months of intervention, the levels of plasma folate, RBC folate concentration increased while the plasma Hcy concen-tration decreased in all three intervention groups. Although the plasma folate concentration increased the most obvious in TT genotype than that of CC and CT genotypes, P＜0.05), the plasma Hcy concentration decreased the most obvious in TT geno-type than that of CT genotype, P＜0.05). Logistic regression analysis showed that the MTHFR TT genotype was a risk factor of high Hcy concentration, which was 8.078 times compared with that of CC genotype (P＜0.05). Conclusion Folic acid sup-plement can significantly increase plasma folate and red cell folate concentration, and reduce plasma Hcy concentration in all MTHFR genotypes. TT genotype was the most dangerous in disorder of folic metabolic and high Hcy concentration. However, low-dose folic acid supplement cannot reduce the risk of high Hcy concentration.