The ester-based vanadium complexes, bis(methylacetoacetato) oxovanadium (IV), bis(ethylacetoacetato) oxovanadium(IV) and bis(ethylbenzoylacetato) oxovanadium(IV), have been prepared and characterized by physicochemical and spectroscopic methods. The biological efficacies of the complexes were investigated. These complexes possess substantial glucose lowering ability and also show improved glucose tolerance effect. © 2010 Springer Science+Business Media B.V.