The vanadium(IV) ion is found to form the [VO(SO4)(H2O)4]·H2O complex, as well as the dimer, [VO(H2O)3]2(μ-SO4)2, in concentrated H2SO4 media. Their formation mechanisms were investigated by UV–Visible spectroscopy (UV–Vis), Raman spectroscopy, X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). UV–Vis spectroscopy study showed that [VO(SO4)(H2O)4]·H2O concentration in H2SO4 solution was proportional to concentrations of VO2+ and SO4 2−. The increased deviation from the near centrosymmetry of the octahedral complexes is due to the replacement of an equatorial water oxygen in [VO(H2O)5]SO4 by a sulfate oxygen in [VO(SO4)(H2O)4]·H2O. The dimer shows symmetrical structure, which correlates very well with non-activity in UV–Vis spectroscopic analysis. Structural information on both vanadium(IV) species can be confirmed by Raman and XRD measurements of crystals from the supersaturated solution of VOSO4 in 1M, 6M and 12M sulfuric acid. A solution of vanadium(IV) (0.05M) in 12M H2SO4, in which the vanadium(IV) species is [VO(H2O)3]2(μ-SO4)2, exhibits a reversible redox behavior near 1.14V (vs. SCE) on the carbon paper electrode.