The hepatoprotective effects of the water extracts of Hovenia dulcis Thunb (HD) were investigated in vitro. Following the induction of hepatotoxicity by ethanol in primary cultures of rat hepatocytes, the protective effects of four different water extracts of HD were determined through serial dose-response and time-dependent studies. The individual extracts used in these studies were prepared from fruits, seeds, leaves and tubes. Treatment of hepatocyte cultures with the water extracts of HD provided a significant protection from the increased lactate dehydrogenase activity induced by ethanol. Particularly, the fruits extract was the most effective against ethanol-induced hepatotoxicity in the primary cultures of rat hepatocytes. The results demonstrated that the extracts might have the protective effect against ethanol-induced toxicity in hepatocyte cultures.