The effect of Haeamtang (HAT) on the colon cancer HT-29 cells was investigated in this study. A water extract of HAT significantly decreased the number of HT-29 cells in a dose-and time-dependent manner as determined by a MTT assay. Flow cytometry results revealed a dose- and time-dependent increase of dead cells in HT-29 cells treated with HAT extract. The anticancer activity of the H AT extract is attributed to apoptosis induced in HT-29 cells, which was demonstrated by increased caspase-3 activity and poly-ADP-ribose polymerase fragmentation. A selective caspase inhibitor, z-VAD-fmk, inhibited the HAT-induced cell death. Taken together, these results demonstrate that HAT extract induces apoptosis in HT-29 cells.