Biosynthetic pathways of Lewis antigens with type 1 and type 2 chains were described on the molecular genetic basis of glycosyltransferases involved in synthesis of the antigens. The analysis of Lewis-gene (Le gene) genotyping revealed that the Le gene is responsible not only for synthesis of Lewis antigens on erythrocytes (Le(a) and Leb antigens) but also for synthesis of the Lewis antigens with type 1 chain, Le(a), Leb and sLea antigens, in digestive organs. Among an a1,3 fucosyltransferase family, FucT VI is a candidate more responsible for synthesis of sLex antigen in intestinal cancer cells than the other a1,3 fucosyltransferases. Molecular genetic analysis on Se gene is now under progress to distinguish the genotypes of Le (a+ b-) individuals from Le(a- b+) individuals in the Japanese population. Individual polymorphism of Lewis antigens is determined by point mutations of glycosyltransferase genes, as proved in ABO, Le, Se, H and FucT VI genes, involved in biosynthetic pathways of the antigens.