Abstract The aim of the present work is to elucidate the role played by lithium impurities in the D 2O adsorption on MgO(1 0 0) surfaces at room temperature and on H and D diffusion processes by using electron stimulated desorption (ESD). The growth of the D 2O layer has been studied by recording the intensity of O +, OD + and D + desorbed ions. Whereas for undoped MgO surfaces the O + intensity decreases with coverage, in Li-doped MgO surfaces the intensity increases. These findings together with the observed threshold energy of D + desorbed ions at 55±5 eV indicate that adsorbed D 2O undergoes preferentially total dissociation on the MgO : Li system. This threshold energy corresponds to the Mg 2p excitation, which means that the D species are bonded to the Mg atoms.