Effects of oxygen vacancy (Vo) on magnetic properties of Co-doped ZnO were investigated by first principle calculations. The calculated formation energies of Vo with different bonding to Co atom indicate that Vo prefers location near Co atom, implying a strong local interaction between the Co atom and O-vacancy. Induced by Vo, the Co-3d and O-2p valence bands upward shift towards the Fermi level, leading to the presence of additional carriers at the Fermi level. The delocalized carriers and the substitutional Co ion played a key role in the occurrence and stability of ferromagnetism of Co-doped ZnO.Effects of Oxygen Vacancy on Magnetic Properties of Cobalt-Doped ZnO Dilute Magnetic Semiconductors. Tao, H.L., Zhang, Z.H., Pan, L.L., He, M., Song, B., Li, Q.: International Journal of Modern Physics B, 2013, 27[17], 1350078