Epigenetics may influence the expression of numerous genes, which might contribute to autoimmune diseases. DNA methylation is mediated by DNA methyltransferases, especially DNA methyltransferase 3B (DNMT3B). Polymorphisms of the DNMT3B gene may influence DNMT3B activity on DNA methylation and increase the susceptibility to several diseases. The current study investigated the association between DNMT3B 579G>T and the risk for idiopathic thrombocytopenic purpura (ITP). The DNMT3B 579G>T polymorphisms were analyzed by PCR-RFLP. There was no significant difference in genotype and allele distribution between the ITP patient and the controls (p = 0.722 and 0.667, respectively). Similar results were observed between the 2 groups when stratified by age and disease course, including acute in childhood, chronic in childhood, acute in adult and chronic in adult. Importantly, this study showed a statistical difference in the distribution of SNP of DNMT3B between Chinese and Koreans or Americans. It is shown that the SNP of DNMT3B 579G>T may not be used on its own as a marker to predict the susceptibility to ITP in a Chinese population and that DNMT3B 579G>T promoter SNP varies from one ethnic population to another.