The extracts were prepared from ripe blackberries. The extracts were tested against the human hepatocellular carcinoma cell line, HepG2, and the mouse cell line L₂₀B using a neutral red assay. The extracts showed a clear inhibition rate, in a dose dependent manner in both cell lines. In addition, the inhibition rate was significantly higher (P < 0.05) for alcoholic extracts in both cell lines compared to aqueous extracts. The results clearly show that Rubus idaeus fruit extracts have potent cytotoxic and cytostatic effects on both cell lines. On the basis of these results, we can conclude that Rubus idaeus has a strong cytotoxic effect on both human and mouse cancerous cells.