Abstract: The electron spin resonance (ESR) spectra of varying quantities of vanadyl ion (VO2+) adsorbed on hydrated hectorite indicated that hydrolysis of VO2+ was promoted at low levels of adsorption. The hydrolyzed product was adsorbed on the clay surfaces, with a ligand environment that was partially aqueous and partially hydroxide in nature. Greater amounts of VO2+ adsorbed on wetted hectorite obscured the ESR spectrum of the strongly adsorbed hydrolysis product with a solutionlike spectrum. An approximately 50% reduction in rotational mobility of VO2+ relative to solution was indicated by the linewidth of this spectrum. Loss in mobility occurred with reduction of the interlamellar spacing until, under strongly dehydrating conditions, the VO(H2O)52+ ions became aligned with the V=O bond axis normal to the plane of the clay platelets.