Infrared spectra of NH and ND stretch bands of the 7-azaindole (7-AI) dimer and its tautomeric dimer are observed to investigate a deuteration effect on the spectra and also a ground-state double proton-transfer (DPT) reaction. We examined the three isotopic species for each dimers; undeuterated one (NH–NH) and one or two hydrogen atom(s) of the NH groups is deuterated ones (NH–ND and ND–ND, respectively). It is found that the ND stretch band profiles of the NH–ND and ND–ND tautomeric dimers are very similar with each other. This result is very distinct from the result of the comparison of the NH stretch band profiles of the NH–NH and NH–ND dimers in our previous paper. For a further discussion, we examined the deuteration effect in the case of the 7-AI dimer. It is found that band profiles of the NH stretch of the NH–NH and the NH–ND dimers and also the ND stretch of the NH–ND and the ND–ND dimers exhibit similar patterns, respectively. These facts indicates that the vibrational relaxation from the NH/ND stretch level of the dimer basically proceed within a monomer unit. The large deuteration effect of the NH stretch band profile observed previously is found to be characteristic of the tautomeric dimer. This behavior is related to a large anharmonicity of the potential energy surface originating from an existence of the double-proton transfer reaction barrier.