Large mafs are transcriptional factors and members of the basic leucine zipper (b-Zip) superfamily. Since we previously identified expression of c-maf in mouse kidney, we presently investigated the mRNA expression profile in the kidney of c-maf gene knockout mice by using DNA microarray, and plasma glutathione peroxidase-3 (GPx3) was predominantly downregulated. We focused on the relation between the expression level of c-maf and GPx3 in vivo and in vitro. Since GPx3 is an antioxidant enzyme, oxidative stress was induced by exposing a culture cell derived from mouse renal tubules (mIMCD3) to hydrogen peroxide. Real-time PCR demonstrated that mRNA expression of both c-maf and GPx3 increased in parallel during exposure to oxidative stress in a time- and dose-dependent manner. Then, the mIMCD3 cells were transfected with c-maf-cDNA containing plasmid, which resulted in an increase in mRNA and protein expression of GPx3 compared with the control cells. Thus, c-maf may be transcriptional regulator of GPx3 expression and modulate the antioxidative pathway in the kidney.