We present an electrical impedance based biosensor on a microfluidic cell culture platform that enables label-free and re- al-time investigation of drug toxicity-induced effects on hepatocytes. The temporal evolution of the impedance at different frequencies strongly suggests distinct information on toxicity effects within the cell culture. The findings indicate that the sen- sor distinguishes between morphological changes and severe cell injury within a cell population owing to the combination of high-density culture, perfusion flow and whole impedance-frequency spectrum analysis. More importantly, cellular changes can be sensed long before cellular death, offering a highly sensitive technique over standard viability assays.