Orostachys japonicus (O. japonicus), used to treat diseases such as various cancers, gastric ulcers, fever, hepatitis, arthritis, eczema, for hemostasis, and intoxication in folk medicine, has been an important constituent in many herbal formulae. We demonstrated that the water extract of O. japonicus led to growth inhibition of LX2 cells by inducing apoptosis through the caspase activation, related to the MAPK pathway. O. japonicus inhibited proliferation of LX2 cells in a dose- and time-dependent manner, increased the apoptosis fraction at cell cycle progression with an accompanying DNA fragmentation, and resulted in a significant decrease in Bcl-2 and an increase in Bax mRNA levels. Exposure of LX2 cells to O. japonicus induced caspase-3 activation, however when the LX2 cells were also treated with the pan-caspase inhibitor Z-VAD-FMK and the caspase-3 inhibitor Z-DEVE-FMK, apoptosis was blocked. O. japonicus inhibited anti-apoptotic Mcl-1 protein and MEK/ERK phosphorylation in LX2 cells. The results indicate that O. japonicus inhibits the cell growth of LX2 cells by inducing apoptosis through caspase activity. O. japonicus down-regulated Mcl-1 protein levels and inhibited the phosphorylation of MEK/ERK, suggesting that it mediates cell death in LX2 cells through the down-regulation of Mcl-1 protein via a MEK/ERK-independent pathway.