UV and ESR Spectra of organometallic complexes formed by the reaction of vanadyl ion with various hydroxamic acids in dioxane were observed. These results reflect the good relationship between planarity of complexes and vanadyl hyperfine coupling constants. Vanadyl-hydroxamic acid complexes prefer planar tetra-coordination comfomation are seem to show the similar behavior as copper-hydroxamic acid complexes. However, by one-electron oxidation, vanadyl ions produced corresponding nitroxide radicals in hydroxamic acids. The ability of vanadyl ion for radical production is suggested to be involved in the similar mechanism detected in metabolism.