Rhus verniciflua Stokes (RVS) has been used as a traditional herbal medicine. Several earlier studies indicated that an ethanol extract of RVS has both anti-oxidant and anti-tumor properties, although the mechanism for the activity remains to be elucidated. In this report, we prepared a highly purified ethanol extract from RVS, named REEE-1 (Rhus ethanol eluted extract-1), and investigated the mechanism involved in its growthinhibitory effect on the human B and T lymphoma cell lines, BJAB and Jurkat, respectively. Results from tritium uptake proliferation assays showed that the proliferative capacities of both BJAB and Jurkat cells were strongly suppressed in the presence of REEE-1. This was further confirmed through trypan blue exclusion experiments that revealed a dose-dependent decrease in viable cell numbers after REEE-1 treatment. REEE-1-mediated suppression of cell growth was verified to be apoptotic, based on the increase in DNA fragmentation, low fluorescence intensity in nuclei after propidium iodide staining, and the appearance of DNA laddering. In particular, REEE-1 exerted its anti-oxidant activity through the inhibition of hydroxyl radical-mediated degradation by iron ion chelation rather than direct scavenging of hydroxyl radicals. Furthermore, REEE-1 was revealed to be a potential scavenger of superoxide anions. Collectively, our findings suggest that REEE-1 is a natural anti-oxidant that could be used as a cancer chemo-preventive and therapeutic agent.