Dicitrinone　B,　a　rare　carbon-bridged　citrinin　dimer,　was　isolated　from　the　marine-derived　fungus,　Penicillium　citrinum.　It　was　reported　to　have　antitumor　effects　on　tumor　cells　previously;　however,　the　details　of　the　mechanism　remain　unclear.　In　this　study,　we　found　that　dicitrinone　B　inhibited　the　proliferation　of　multiple　tumor　types.　Among　them,　the　human　malignant　melanoma　cell,　A375,　was　confirmed　to　be　the　most　sensitive.　Morphologic　evaluation,　cell　cycle　arrest　and　apoptosis　rate　analysis　results　showed　that　dicitrinone　B　significantly　induced　A375　cell　apoptosis.　Subsequent　observation　of　reactive　oxygen　species　(ROS)　accumulation　and　mitochondrial　membrane　potential　(MMP)　reduction　revealed　that　the　apoptosis　induced　by　dicitrinone　B　may　be　triggered　by　over-producing　ROS.　Further　studies　indicated　that　the　apoptosis　was　associated　with　both　intrinsic　and　extrinsic　apoptosis　pathways　under　the　regulation　of　Bcl-2　family　proteins.　Caspase-9,　caspase-8　and　caspase-3　were　activated　during　the　process,　leading　to　PARP　cleavage.　The　pan-caspase　inhibitor,　Z-VAD-FMK,　could　reverse　dicitrinone　B-induced　apoptosis,　suggesting　that　it　is　a　caspase-dependent　pathway.　Our　data　for　the　first　time　showed　that　dicitrinone　B　inhibits　the　proliferation　of　tumor　cells　by　inducing　cell　apoptosis.　Moreover,　compared　with　the　first-line　chemotherapy　drug,　5-fluorouracil　(5-Fu),　dicitrinone　B　showed　much　more　potent　anticancer　efficacy,　suggesting　that　it　might　serve　as　a　potential　antitumor　agent.　©　2014　by　the　authors;　licensee　MDPI.