The present study was aimed at determining the oxidative damage caused by sodium arsenite in 3T3 fibroblast cells and the possible protective role of curcumin (Cur) against sodium arsenite toxicity. Embryonic fibroblast cells were exposed to sodium arsenite (0.01, 0.1, 1, and 10 mu M) in the presence and absence of Cur (2.5 mu M) for 24 hours. Cell viability, cytotoxicity, lipid peroxidation, hydroxyl radical, hydrogen peroxide, antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase) and expression levels of antioxidant genes (superoxide dismutase, catalase, and glutathione peroxidase) were measured in embryonic fibroblast cells. Results demonstrated that sodium arsenite directly affects antioxidant enzymes and genes in 3T3 embryonic fibroblast cells and induces oxidative damage by increasing the amount of hydrogen peroxide, hydroxyl radical, and lipid peroxidation in the cell. Furthermore, the study indicated that Cur might be a potential ameliorative antioxidant to protect the fibroblast cell toxicity induced by sodium arsenite.