The mood-stabilizing drug lithium is the most commonly used treatment for bipolar disorder. Previous studies have shown that chronic treatment with lithium produces a protective effect against oxidative stress. Nuclear factor E2-related factor 2 (Nrf2) is a gene transcription factor that binds to the electrophile response element (EpRE) and triggers expression of various genes with antioxidant properties. Nrf2 contributes significantly to cytoprotection against oxidative stress. The purpose of this study is to determine the role of Nrf2 in the protective effect of lithium against oxidative stress. We found, using immunoblotting analysis, that chronic, but not acute treatment with lithium increased nuclear levels of Nrf2 in rat pheochromocytoma PC12 cells. DNA pull-down assay has shown that Nrf2 can bind to a double-strained oligonucleotide containing an EpRE site from glutathione s-transferase A4. Electrophorectic gel shift analysis further showed that chronic treatment with lithium increased Nrf-2-EpRE binding activity. We also found that knocking down Nrf2 with its short hairpin RNA inhibited lithium-increased expression of Nrf2 and suppressed the protective effect of lithium against hydrogen peroxide (H₂O₂)-reduced cell viability and H₂O₂-increased DNA fragmentation. Because Nrf2 can induce expression of various genes that play important roles in cytoprotection, the current findings suggest that Nrf2 may mediate the neuroprotective effect of lithium against oxidative stress.