The Caesalpinia sappan is widely used in the traditional oriental herbal medicine for anti-inflammatory, antioxidant effects. The effects of water extract of C. sappan on the cell viability and induction of apoptosis were investigated in human lung cancer cell line A549. The water extract of C. sappan produced apoptotic cell death and DNA fragmentation and nucleus chromatin condensation in A549 cells. The enzyme activity of caspase-3 and protein level of actived caspase-3 were markedly increased in A549 cells treated with the water extract of C. sappan. In addition, the extract of C. sappan induced cleavage of Poly (ADP-ribose) polymerase (PARP), a known substrate for caspase-3, and dropped in cellular ATP levels. These results suggest that the extract of C. sappan exerts anticancer activity by induction of apoptosis via activation of caspase-3, cleavage of PARP protein, and depletion of cellular ATP levels in A549 cells.