Epigallocatechin-3-gallate (EGCG) is the most abundant polyphenol molecule from green tea and is knownto exhibit antioxidative as well as tumor suppressing activity. In order to examine EGCG tumor invasion andsuppressing activity against adult T-cell leukemia (ATL), two HTLV-1 positive leukemia cells (HuT-102 and C91-PL) were treated with non-cytotoxic concentrations of EGCG for 2 and 4 days. Proliferation was significantlyinhibited by 100 μM at 4 days, with low cell lysis or cytotoxicity. HTLV-1 oncoprotein (Tax) expression in HuT-102 and C91-PL cells was inhibited by 25 μM and 125 μM respectively. The same concentrations of EGCGinhibited NF-kB nuclearization and stimulation of matrix metalloproteinase-9 (MMP-9) expression in both celllines. These results indicate that EGCG can inhibit proliferation and reduce the invasive potential of HTLV-1-positive leukemia cells. It apparently exerted its effects by suppressing Tax expression, manifested by inhibitingthe activation of NF-kB pathway and induction of MMP-9 transcription in HTLV-1 positive cells.