The　Hartree-Fock　method　and　density　functional　theory　(B3LYP　method)　at　the　6-31G(d)　basis　set　level　were　used　to　determine　the　molecular　geometrical　parameters　and　hydrogen　bonding　energies　of　oxo　form　(Py)　and　hydroxy　form　(Hy)　tautomers　of　2-hydroxy　pyridine,　dimers　and　hydrated　complexes.　Five　complexes,　Hy...H2O,　Py...H2O,　Hy...Hy,　Py...Py　and　Hy...Py,　were　computed　in　this　study.　The　DFT　and　ab　initio　HF　predicted　results　for　Py　are　in　agreement　with　the　available　experimental　values.　The　calculations　also　show　that　Py　become　more　stable　than　Hy　in　water.　The　dissociation　energies　mainly　due　to　the　stabilization　energy　associated　from　the　dual　hydrogen-bonding　formation　were　calculated　as　the　change　in　the　molecular　enthalpy　of　formation　in　the　conversion　of　the　monomers　individually　into　the　dimers　or　hydrated　tautomers.　For　the　dissociation　energy,　the　results　indicate　that　the　hydrated　tautomers　of　Hy　and　Py　are　smaller　than　those　of　their　dimers.　The　dissociation　energies　predicted　at　the　B3LYP/6-31G(d)　level　for　the　five　complexes　corrected　by　the　basis　set　superposition　error　(BSSE)　and　zero　point　vibrational　energy　(ZPVE)　are　38.3,　40.8,　73.0,　82.7　and　71.1　kJ/mol,　respectively.