This study was conducted to investigate the anti-proliferative activities of medicinal mushroom Ganoderma lucidum (Rei-shi or Mannentake). We have identified an alcohol extract from the spore of Ganoderma lucidum that inhibits the in vitro proliferation of human umbilical vein endothelial cells and MDA-MB231 human breast cancer cells. Further fractionation of the alcohol extract revealed that the ethyl acetate fraction inhibited both cell lines in a dose-dependent manner from 2 to 40 micro g/ml. Our results suggest that the alcohol extract from the spore of Ganoderma lucidum may possess potential anti-tumor and anti-angiogenic activities.