Arsenic (+3 oxidation) methyltransferase (AS3MT) is the key enzyme in biotransformation pathway of inorganic arsenic. To early evaluate the variation of AS3MT polymorph isms, PCR-RFLP technology was ultilized. In this study, the homozygote for SNP 14458TT (rs11191439) and heterozygote for SNP 4602AG (rs7085104) were detected in all templates, whereas heterozygote Tạp chí and homozygote TT appeared in control and arsenic exposured templates in SNP 5913 (rs4917986), respectively. Altoghether, the results are premise for further studies on genetic polymorphisms of pre-born arsenic exposured in infants.