KDM6B/JMJD3 is a histone H3 lysine demethylase with an important gene regulatory role in development and physiology. Here, we show that human JMJD3 expression is induced by the active vitamin D metabolite 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) and that JMJD3 modulates the gene regulatory action of this hormone. 1,25(OH)2D3 activates the JMJD3 gene promoter and increases the level of JMJD3 RNA in human cancer cells. JMJD3 upregulation was strictly dependent on vitamin D receptor (VDR) expression and was abolished by cycloheximide. In SW480-ADH colon cancer cells, JMJD3 knockdown or expression of an inactive mutant JMJD3 fragment decreased the induction by 1,25(OH)2D3 of several target genes and of an epithelial adhesive phenotype. Moreover, JMJD3 knockdown upregulated the epithelial-to-mesenchymal transition inducers SNAIL1 and ZEB1 and the mesenchymal markers fibronectin and LEF1, while it downregulated the epithelial proteins E-cadherin, Claudin-1 and Claudin-7. Additionally, JMJD3 knockdown abolished the nuclear export of β-catenin and the inhibition of β-catenin transcriptional activity caused by 1,25(OH)2D3. Importantly, the expression of JMJD3 correlated directly with that of VDR and inversely with that of SNAI1 in a series of 96 human colon tumours. Our results indicate for the first time that an epigenetic gene coding for a histone demethylase such as JMJD3 is a VDR co-target that partially mediates the effects of 1,25(OH)2D3 on human colon.