In the present study, vibrational properties of the C-alpha-D stretching mode in deuterated alanine dipeptide are examined by ab initio normal-mode calculations. A backbone conformational scan reveals a quite similar structural sensitivity of the harmonic and anharmonic vibration frequencies for both the fundamental and overtone transitions. The distributions of the frequencies are found to be linearly anticorrelated with that of the C-alpha-D bond length, with the latter being found to be also structurally sensitive. Theory predicts that, as determined by the quantum mechanical anharmonic force field, the highly anharmonic (with a mean diagonal anharmonicity of 48.0 cm(-1)) and yet highly localized C-alpha-D stretching mode shall be potentially useful in probing peptide local structures and dynamics.