The objective of this study is to evaluate the efficacy of epigallocatechin gallate against ATL cells. The anti-proliferative and pro-apoptotic effects of EGCG were evaluated in HTLV-1-positive and -negative cells. EGCG exhibited a marked decrease in proliferation of ATL cells at 96 h of treatment. The results indicated that TGF-α was down-regulated whereas levels of TGF-β2 increased. Cell cycle distribution analysis revealed an increase in cells in the pre-G1 phase which was confirmed by ELISA. The results on proteins showed an up-regulation of p53, Bax and p21 protein levels while the levels of Bcl-2α were down-regulated.