The　Monascus　pigment,　rubropunctatin,　was　extracted　and　purified　from　red　mold　rice　(RMR)　and　its　cytotoxic　activities　against　human　gastric　adenocarcinoma　BGC-823　cells　were　studied　both　in　vitro　and　in　vivo.　Rubropunctatin　inhibited　the　proliferation　of　BGC-823　cells　with　an　inhibitory　concentration　(IC50)　of　12.57　mu　M,　while　it　exhibited　no　significant　toxicity　to　normal　gastric　epithelial　cell　GES-1　at　the　same　concentration.　Treatment　of　BGC-823　cells　with　rubropunctatin　resulted　in　a　dose-　and　time-dependent　apoptosis,　as　validated　by　the　increase　in　the　percentage　of　cells　in　sub-G1　phase　and　phosphotidylserine　externalization.　The　in　vivo　experimental　data　demonstrated　that　rubropunctatin　could　offer　similar　therapeutic　benefits　in　comparison　with　the　same　dose　of　taxol.　After　five　times　of　intravenous　injection,　tumor　weight　in　BGC-823-bearing　nude　mice　reduced　23.5%　at　the　dose　of　8　mg/kg　and　37.7%　at　the　dose　of　32　mg/kg,　respectively.　The　expressions　of　30　genes　related　to　induction　of　apoptosis　were　found　up-regulated　significantly.　The　two　most　expressed　genes　were　tumor　necrosis　factor　(TNF)　and　DNA-damage　inducible　transcript　3.　TNF　was　considered　as　a　major　mediator　of　apoptosis　induced　by　rubropunctatin.　This　is　the　first　report　describing　the　anti-proliferative　effect　of　rubropunctatin　and　its　apoptosis　mechanism　on　BGC-823　cells.　Rubropunctatin　has　potential　to　be　developed　as　a　new　natural　anti-cancer　agent.