In this work the binding of V IV O 2+ and V IV O-complexes to serum albumins {human serum albumin (HSA), bovine serum albumin (BSA) and porcine serum albumin (PSA)} are studied using circular dichroism (CD), electron paramagnetic resonance (EPR) and visible absorption spectroscopy. The results confirm previous findings that V IV O 2+ occupies at least two types of binding sites on albumin: 'the strong vanadium binding site' (designated by VBS1) and 'the weak vanadium binding sites' (designated by VBS2). VBS1 binds 1 mol equivalent of V IV O 2+ . On the other hand VBS2 correspond to binding of several mol equivalents of V IV O, and studies done with PSA in the presence of excess Zn II ions indicate that VSB2 corresponds to two distinct types of sites. The hyperfine coupling constant Az for V IV O 2+ binding at VBS2 on HSA and BSA are all very similar (~168 × 10 -4 cm -1 ) but differ slightly on PSA (~166 × 10 -4 cm -1 ) due to differences in the binding sets. When (V IV O)-HSA systems are titrated with maltol ternary species of (maltol)m(V IV O)mHSA and (maltol)2m(V IV O)mHSA stoichiometry form which are clearly distinguishable from the binary (V IV O)-HSA system by the type and intensity of the CD spectra recorded. Changes are also observable in the intensity of the X-band EPR spectra, but not much in the hyperfine coupling constants Az, which are all in the range 166-167 × 10 -4 cm -1 . The results further