DNA methylation has been proven to be a critical epigenetic mark important for various cellular processes. Here, we report that redox-Active quinones, a ubiquitous class of chemicals found in natural products, cancer therapeutics and environment, stimulate the conversion of 5mC to 5hmC in vivo, and increase 5hmC in 5751 genes in cells. 5hmC increase is associated with significantly altered gene expression of 3414 genes.Interestingly, in quinone-treated cells, labile ironsensitive protein ferritin light chain showed a significant increase at both mRNA and protein levels indicating a role of iron regulation in stimulatingTet-mediated 5mC oxidation. Consistently, the deprivation of cellular labile iron using specific chelator blocked the 5hmC increase, and a delivery of labile iron increased the 5hmC level. Moreover, both Tet1/Tet2 knockout and dimethyloxalylglycine-induced Tet inhibition diminished the 5hmC increase. These results suggest an ironregulated Tet-dependent DNA demethylation mechanism mediated by redox-Active biomolecules. © 2013 The Author(s) 2013. Published by Oxford University Press.