The　present　study　was　conducted　in　order　to　explore　the　mechanisms　whereby　parathyroid　hormone　(PTH)　maintains　in　vitro　proliferation　of　bone　marrow　mesenchymal　stem　cells　(BMSCs).　Bone　marrow　was　isolated　from　Sprague　Dawley　(SD)　rat　femurs,　cultured　in　vitro,　and　passaged　using　a　cell　adherent　culture　method.　The　BMSC　proliferation　was　evaluated　by　the　methyl　thiazolyl　tetrazolium　(MTT)　assay　and　the　fluorescence　intensity　of　calcium　ions　in　BMSCs　was　analyzed　by　laser　scanning　confocal　microscopy　(LSCM).　Our　results　show　that　BMSC　proliferation　in　the　experimental　group　treated　with　PTH　was　more　significant　than　controls.　The　calcium　ion　fluorescence　intensity　in　BMSCs　was　significantly　higher　for　the　experimental　group　as　compared　to　the　control　group.　For　each　group,　there　was　significant　difference　in　the　fluorescence　intensity　of　calcium　ions　in　BMSCs　between　7　d　and　14　d.　In　conclusion,　parathyroid　hormone　increased　the　fluorescence　intensity　of　calcium　ions　in　BMSCs,　which　might　represent　a　key　mechanism　whereby　BMSC　proliferation　is　maintained.