Backgrounds: A promising and important group of potential cancer preventive agents are those derived from natural products. Recent studies revealed various biological activities including the antitumor properties of exopolysaccharides produced by macrofungus. Edible mushrooms are a valuable source of biologically active compounds. Mushrooms demonstrate their efficiency against numerous diseases and metabolic disturbances as serious as cancer. The most significant medicinal effects of mushrooms and their metabolites that have attracted the attention of the public is their antitumor properties. The oyster mushroom (Pleurotus ostreatus) is one of the widely cultivated edible mushrooms. Lung and colon cancers continue to be the most common cancers. Purpose: In this study, we aimed to determine the antiproliferative and antimetastatic effects of Pleurotus ostreatus ethanol extract on A549 human non-small lung cancer and Caco-2 colon cancer cells. Methods: To evaluate anticancer potential of the Pleurotus ostreatus extract, the methods measuring various antiproliferative endpoints were employed including MTT assay, real time monitoring of cell proliferation, anti-invasion and anti-migration with real time cell analyzer system. Results: The cytotoxic effects of different concentrations of the extract were investigated on both cancer cells and then IC50 values were calculated. Cell proliferation assay was performed with IC50 concentrations of the extract (21.6 ?g/mL for Caco2 and 38.7 ?g/mL for A549 cells). Conclusions: Extract of Pleurotus ostreatus was induced cell death and antimetastatic activities of both cancer cells, especially A549 lung cancer.