Aim:　To　study　the　growth　inhibitory　and　apoptotic　effects　of　Scutellaria　barbata　D.Don　(5　barbata)　and　to　determine　the　underlying　mechanism　of　its　antitumor　activity　in　mouse　liver　cancer　cell　line　H22.　METHODS:　Proliferation　of　H22　cells　was　examined　by　MTT　assay.　Cellular　morphology　of　PC-2　cells　was　observed　under　fluorescence　microscope　and　transmission　electron　microscope　(EM).　Mitochondrial　transmembrane　potential　was　determined　under　laser　scanning　confocal　microscope　(LSCM)　with　rhodamine　123　staining.　Flow　cytometry　was　performed　to　analyze　the　cell　cycle　of　H22　cells　with　propidium　iodide　staining.　Protein　level　of　cytochrome　C　and　caspase-3　was　measured　by　semi-quantitive　RT-PCR　and　Western　blot　analysis.　Activity　of　caspase-3　enzyme　was　measured　by　spectrofluorometry.　RESULTS:　MTT　assay　showed　that　extracts　from　5.　barbata　(ESB)　could　inhibit　the　proliferation　of　H22　cells　in　a　time-dependent　manner.　Among　the　various　phases　of　cell　cycle,　the　percentage　of　cells　in　S　phase　was　significantly　decreased,　while　the　percentage　of　cells　in　G,　phase　was　increased.　Flow　cytometry　assay　also　showed　that　ESB　had　a　positive　effect　on　apoptosis.　Typical　apoptotic　morphologies　such　as　condensation　and　fragmentation　of　nuclei　and　blebbing　membrane　of　apoptotic　cells　could　be　observed　under　transmission　electron　microscope　and　fluorescence　microscope.　To　further　investige　the　molecular　mechanism　behind　ESB-induced　apoptosis,　ESB-treated　cells　rapidly　lost　their　mitochondrial　transmembrane　potential,　released　mitochondrial　cytochrome　C　into　cytosol,　and　induced　caspase-3　activity　in　a　dose-dependent　manner.　CONCLUSION:　ESB　can　effectively　inhibit　the　proliferation　and　induce　apoptosis　of　H22　cells　involving　loss　of　mitochondrial　transmembrane　potential,　release　of　cytochrome　C,　and　activation　of　caspase-3.　(c)　2008　The　WJG　Press.　All　rights　reserved.