MP2　and　DFT/B3LYP　calculations　with　Aug-cc-pvTz　and　Aug-cc-pvQz　basis　set　levels　are　used　to　investigate　the　equilibrium　structures　and　isomerization　of　H2SO　isomers.　All　of　the　transition　states　have　been　calculated　and　confirmed　by　the　intrinsic　reaction　coordinate　(IRC).　The　calculated　results　show　that　H2SO　isomers　have　three　equilibrium　structures　and　the　linear　structure　is　the　most　stable　while　the　branched　H2OS　is　the　most　unstable　(the　relative　energies　are　0.0,　82.1　and　155.3　kJ/mol　for　HSOH,　H2SO　and　H2OS,　respectively　with　the　zero　point　vibrational　energy　correction　at　B3LYP/Aug-cc-pvQz　level).　It　is　difficult　for　the　linear　HSOH　to　convert　to　the　branched　H2SO　and　H2OS　isomers　due　to　the　high　activation　energies　(higher　than　ca.　200　and　160　kJ/mol,　respectively).　The　predicted　thermodynamic　results　also　suggest　that　the　linear　structure　is　the　most　stable　and　may　be　the　only　species　that　can　be　found　experimentally.　The　kinetic　results　demonstrate　that　the　isomerization　is　a　unimolecular　one,　and　the　reaction　rate　is　slow.