Ethanol decomposition on Rh(111) is systematically investigated using periodic density functional theory(DFT) calculations. The various adsorption modes of the intermediates involved are located. It is determined that ethanol adsorbs weakly on the Rh(111) surface. CH3CH2O, CH, and H prefer 3-fold sites with adsorption energies of 49.9, 146.6, and 64.3 kcal/mol, respectively. CO binds stably at the top site with a binding energy of 42.5 kcal/mol. CH2CH2O (3-fold-η1(C)-η1(O)) and CHCO (3-fold-η2(C)-η1(CR)) are inclined to adsorb on the surface to make the C and O atoms saturated. For the other intermediates, adsorption configurations are bridge-η1(C)-η1(O) for CH2CHO, 3-fold-η1(C)-η1(CR)-η1 (O) for CH2CO, and 3-fold-η2(C)-η1(O)for CHCHO. For intermediates going along the decomposition pathway, energy barriers for the C-H and C-C bond scission are gradually decreased; however, for the CR-H or C-O bond cleavage, the energy barrier decreases first and then rises, presenting a V-shaped curve. The most favorable decomposition route for ethanol on Rh(111) is CH3CH2OH f CH3CH2O f CH2CH2O f CH2CHO f CH2CO f CHCO f CH +CO f C + CO, in which the dehydrogenation of CH3CH2O is the rate-determining step.