Seventeen　novel　emodin　derivatives　were　synthesized,　and　the　structures　were　confirmed　by　IR,　H　NMR,　MS,　and　elemental　analysis.　The　cytotoxic　activity　of　the　derivatives　was　evaluated　against　A375,　BGC-823,　HepG2,　and　HELF　cells　by　MTT　assay.　Compound　9a　with　highest　potency　and　low　toxicity　was　selected　to　further　investigate　its　detailed　molecular　mechanism.　The　lead　compound　9a　induced　a　loss　of　the　mitochondrial　transmembrane　potential　(Delta　Psi　m),　an　increase　in　reactive　oxygen　species　(ROS),　release　of　cytochrome　c　and　activation　of　caspase-3　and　caspase-9.　In　addition,　the　confocal　study　showed　that　emodin　derivative　9a　(containing　asymmetric　hydrocarbon　tails)　was　mainly　localized　in　mitochondria,　demonstrating　a　key　role　of　the　mitochondria-mediated　apoptosis　pathway　in　cancer　cells.　Taken　together,　the　results　demonstrate　that　embodin　derivative　9a　preferentially　regulates　the　ROS-mediated　apoptosis　in　A375　cells　through　the　induction　of　cytochrome　c　expression　and　activation　of　caspase-3　and　caspase-9　proteins.