In the present study, we investigated the anti-proliferative effects of four tea catechins: (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg) and (-)-epigallocatechin gallate (EGCg) in human T lymphocytic leukemia Jurkat cells. Each catechin induced a significant cytotoxic effect on Jurkat cells. Combinations of EGCg with other catechins additively potentiated anti-proliferation, extracellular hydrogen peroxide formation, c-Jun N-terminal kinase (JNK) activation and interferon (IFN)-gamma mRNA expression. Catalase partly but significantly abolished the cytotoxicity induced by EGC or EGCg, whereas it did not influence the EC- or ECg-induced effect. Among the tea catechins, ECg synergistically enhanced the EGCg-induced JNK phosphorylation and IFN-gamma expression. The present findings provide evidence that tea catechins are able to concertedly induce cytotoxicity through the JNK/IFN-gamma pathway in both a hydrogen peroxide-dependent and -independent manner.