We have investigated the decomposition of ethanol (EtOH) on a 3Ni/alpha-Al2O3(0001) surface using periodic density functional theory calculations. A triangular Ni trimer doped on a 2 x 2 alpha-Al2O3(0001) surface was used to represent the 3Ni/alpha-Al2O3(0001) surface. We considered several possible pathways for EtOH decomposition over the 3Ni/alpha-Al2O3(0001) surface, including dehydrogenation and C-C bond cleavage. Our calculated results indicated that (i) the 3Ni/alpha-Al2O3(0001) surface possesses high activity to inhibit coke formation and (ii) the CH2CH2O(a) -> CH2CHO(a) + H-(a) reaction is the rate-determining step for the overall reaction [CH3CH2OH(a) -> CH2(a) + CO(a) + 4 H-(a)] with an energy barrier of 1.20 eV. One feasible channel leading to C-C bond cleavage is weakening of the C-C bond in the stable CH2CO intermediate via transformation of the adsorbed structure to a metastable structure, thereby increasing the coordination number of the two C atoms to the Ni trimer. In addition, we also investigated the nature of the metal-ethanol bonding through scrutiny of density of states (DOS) and electron density difference contour plots. The DOS analysis allowed us to characterize the state interactions between ethanol and the surfaces; the electron density difference plots provide evidence that is consistent with the prediction from DOS analysis.