Galla Rhois is a nest of parasitic bug, Mellaphis chinensis Bell, in Rhus chinensis Mill. Galla Rhois has been used for the therapy of diarrhea, peptic ulcer, hemauria, etc., that showed various antiinflammatory activity, and other biological properties. We studied the effect of Galla Rhois water extract(GRWE). The cytotoxic activity of GRWE in HL-60 cells was increased in a concentration-dependent manner. GRWE was cytotoxic to HL-60 cells, with $IC_50$ of $100{mu}g/m{ell}$. Treatment of GRWE to HL-60 cells showed the fragmentation of DNA in a concentration manner, suggesting that these cells underwent apoptosis. In addition, the flow cytometric analysis revealed GRWE concentration-dependently increased apoptotic cells with hypodiploid DNA content and arrested G1 phase of cell cycle. These results indicate that GRWE may have a possibility of potential anticancer activities. Treatment of HL-60 cells with GRWE was induced activation of caspase-3, caspase-8 and proteolytic cleavage of poly(ADP-ribose) polymerase. Also, caspase-3 was directly activated via caspase-8 activation. GRWE also caused the release of cytochrome c from mitochondria into the cytosol. GRWE-induced cytochrome c release was mediated by caspase-8-dependent cleavage of Bid and Bax translocation. These results suggest that caspase-8 mediates caspase-3 activation and cytochrome c release during GRWE-induced apoptosis in HL-60 cells.