In this study, facile preparation of pure and nano-sized cobalt oxides particles was achieved using low-cost mechanical ball-milling synthesis route. Microstructural and morphological properties of synthesised products were characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD results indicated that the fabricated samples composed of cubic pure phase CoO and Co3O4 nanocrystalline particles with an average crystallite size of 37.2 and 31.8nm, respectively. TEM images showed that the resulting samples consisted of agglomerates of particles with average diameter of about 37.6nm for CoO and 31.9nm for Co3O4. Phase purity of the prepared samples was further investigated due to their promising technological applications. Local atomic structure properties of the prepared nanoparticles were probed using synchrotron radiation-based X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). EXAFS data analysis further confirmed the formation of single-phase CoO and Co3O4 nanoparticles. In addition, structural properties of cobalt oxide nanoparticles were investigated by performing density functional theory calculations at B3LYP/TZVP level and Born-Oppenheimer molecular dynamics. Theoretical calculations for both prepared samples were found to be consistent with the experimental results derived from EXAFS analysis. Obtained results herein reveals that highly crystalline and pure phase CoO and Co3O4 nanoparticles can be synthesised using simple, inexpensive and eco-friendly ball-milling method for renewable energy applications involving fuel cells and water splitting devices.