RORα and RORγ are expressed in human skin cells that produce the noncalcemic <em>20</em>-hydroxyvitamin D3 [<em>20</em>(OH)D3] and <em>20</em>,23-dihydroxyvitamin D3 [<em>20</em>,23(OH)2D3]. Chinese hamster ovary (CHO) cells stably expressing a Tet-on RORα or RORγ expression vector and a ROR-responsive element (RORE)-LUC reporter, and a mammalian 2-hybrid model examining the interaction between the ligand binding domain (LBD) of RORα or RORγ with an LBD-interacting LXXLL-peptide, were used to study ROR-antagonist activities. These assays revealed that <em>20</em>(OH)D3 and <em>20</em>,23(OH)2D3 function as antagonists of RORα and RORγ. Moreover, <em>20</em>(OH)D3 inhibited the activation of the promoter of the Bmal1 and G6pase genes, targets of RORα, and <em>20</em>(OH)D3 and <em>20</em>,23(OH)2D3 inhibited Il17 promoter activity in Jurkat cells overexpressing RORα or RORγ. Molecular modeling using crystal structures of the LBDs of RORα and RORγ revealed docking scores for <em>20</em>(OH)D3, <em>20</em>,23(OH)2D3 and 1,25(OH)2D3 similar to those of the natural ligands, predicting good binding to the receptor. Notably, <em>20</em>(OH)D3, <em>20</em>,23(OH)2D3, and 1,25(OH)2D3 inhibited RORE-mediated activation of a reporter in keratinocytes and melanoma cells and inhibited <em>IL</em>-17 production by immune cells. Our study identifies a novel signaling pathway, in which <em>20</em>(OH)D3 and <em>20</em>,23(OH)2D3 act as antagonists or inverse agonists of RORα and RORγ, that opens new possibilities for local (skin) or systemic regulation.-Slominski, A. T., Kim, T.-K., Takeda, Y., Janjetovic, Z., Broz˙yna, A. A., Skobowiat, C., Wang, J., Postlethwaite, A., Li, W., Tuckey, R. C., Jetten, A. M. RORα and ROR γ are expressed in human skin and serve as receptors for endogenously produced noncalcemic <em>20</em>-hydroxy- and <em>20</em>,23-dihydroxyvitamin D.