Sasang Constitutional Medicine is based on the diversity of Human being and medically developed the response variation to diseases and medicines. The diversity is categorized as four from physiology, pathology, symptoms, to therapy. So that is related the difference of individual characteristics in Western Science. Single nucleotide polymorphism is the basic tool to research genetic polymorphisms. We researched the polymorphism site of MTHFR gene on 1p36.3, which is relatively reported the occlusive vascular disease. In the clinical research of brain infarction, the occurrence was different according to constitution. The 677C/T Polymorphism site of MTHFR was not significantly different in constitution group. But this research was the first trial about the single nucleotide polymorphism according to constitution. The more researchs of many genes are necessary to find the characteristics of constitution.