B3LYP　calculations　of　density　functional　theory　with　the　6-311　+　G(3df,　2p)　basis　set　level　are　used　to　investigate　the　equilibrium　structures　and　intramolecular　rearrangement　reactions　of　the　linear　BrSSCl　and　branched　SSBrCl　isomers.　The　calculated　results　show　that　the　linear　structure　is　more　stable　than　the　branched　structure　(lower　53.　4kJ　.　mol(-1)　corrected　with　zero　point　vibrational　energy)　energetically.　The　calculated　energy　barriers　for　the　intramolecular　bromine　atom　transfer　and　chlorine　atom　transfer　isomerization　processes　are　102.　9kJ　.　mol(-1)　and　115.　3kJ　.　mol(-1),　respectively.　The　kinetic　results　demonstrate　that　the　isomerization　is　a　unimolecular　process,　and　the　reaction　rate　is　slow.　This　agrees　with　thermodynomical　results.　So　the　isomerization　process　should　proceed　via　other　likely　processes.