Hydrazinium mixed metal hydrogenethylenediaminetetraacetate mono hydrates such as [N2H5M1/3Co2/3 (HEDTA)].H2O where M: Ni, Cu orMg have been prepared by the aqueous reaction between the ligand,dihydraziniumdihydrogenethylenediaminetetraacetateand a mixture of respective metal nitrate hydrates in appropriate and accurate ratio. The complexes were characterized by hydrazine and metal analyses, infrared spectra, thermal analysis and X-ray powder diffraction techniques. From the conclusions derived from TG-DTA analyses, attempt were made to prepare mixed metal oxides, metal cobaltities such as magnesiumcobaltite (MgCo2O4), nickel cobaltite (NiCo2O4) and copper cobaltite (CuCo2O4) by decomposing the respective pure crystalline complexes at 600°C.The products obtained were characterized and confirmed by chemical analysis, infrared spectra, X-ray powder diffraction and SEM techniques.