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The optimal structures of twenty-eight hydrogen-bonded complexes, containing one glycine dipeptide molecule and one of the nucleic acid base adenine, thymine, uracil, guanine and cytosine, were obtained at the B3LYP/6-31＋G(d,p) level. The binding energies of these complexes were further evaluated at the CP-corrected MP2/aug-cc-pVTZ level. The site-preferences of the five nucleic acid bases hydrogen bonding to glycine dipeptide are explored. The calculation results show that any of the five nucleic acid bases can hydrogen bond to glycine dipeptide through different binding site. The hydrogen-bonded complexes formed through site A3 of adenine, site T1 of thymine, site U1 of uracil, site C1 of cytosine and site G3 of guanine are the most stable. The stability of the hydrogen-bonded complexes is associated with the enthalpy change of the protonation/deprotonation reaction of the nucleic acid bases. The more negative the enthalpy change of the protonation reaction or the smaller the enthalpy change of the deprotonation reaction, the more stable the hydrogen-bonded complexes.

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