5-hydroxymethylcytosine (5hmC) is a type of DNA modification generated from the oxidation of 5-methylcytosine (5mC) by ten-eleven translocation (TET) enzymes. 5hmC has a distinct distribution in the genome from 5mC. 5hmC levels are positively correlated with gene expression. Alteration of 5hmC levels has been linked to pathological processes such as cancer. However, the biological functions of this modification remain largely unknown. I mainly work on the biochemical study of 5hmC related proteins and methods for 5hmC detection.