In this study, the antioxidizing effect of 2,3-dicaffeoyl-epi-quinic acid (DEQA) was investigated. The antioxidant activity was evaluated by measuring the scavenging effect on DPPH radical and peroxynitrite and the reducing power on ferric ion. DEQA showed a scavenging effect and reducing power comparable to vitamin C used as a positive control. Also, DEQA effectively inhibited production of intracellular reactive oxygen species (ROS) in HT-1080 cells, showing the scavenging ratio of 43.8% even at 10 μM concentration of DEQA after 2 hours in HT-1080 treated with H2O2. In addition to this, DEQA inhibited the production of nitric oxide (NO) very effectively in Raw 264.7 cells. The above results suggest that DEQA has the potential to be developed as a natural antioxidant.