We previously demonstrated that the methylene chloride fraction of Scutellaria barbata suppessed human leukemic U937 cell proliferation by inducing apoptosis. In the present study, we have isolated luteolin from Scutellaria barbata and evaluated its apoptotic mechanism in Lewis lung carcinoma cells. Luteolin inhibited the proliferation of Lewis lung carcinoma cells in a concentration-dependent manner. Luteolin effectively increased the portion of $sub-G_1$ DNA content (apoptotic portion) and apoptotic Annexin-V positive cells in a concentration-dependent manner by FACS analysis. Caspase 9 and caspase 3 were activated and PARP was effectively cleaved by luteolin. It also increased the ratio of Bax to Bcl-2 through the decrease of Bcl-2 expression by Western blotting and reduced mitochondrial membrane potential following TMRE staining. These results suggest that luteolin can induce apoptosis through the mitochondrial mediated pathway.