IL-10 production by Th17 cells is critical for limiting autoimmunity and inflammatory responses. Gene array analysis on Stat6 and T-bet double deficient Th17 cells identified the Th2 transcription factor c-Maf to be synergistically up-regulated by IL-6 plus TGFbeta, and associated with Th17 IL-10 production. Both c-Maf and IL-10 induction during Th17 polarization depended on Stat3, but not Stat6 or Stat1, and mechanistically differed from IL-10 regulation by Th2 or IL-27 signals. TGFbeta was also synergistic with IL-27 to induce c-Maf, and induced Stat1 independent IL-10 expression in contrast to IL-27 alone. Retroviral transduction of c-Maf was able to induce IL-10 expression in Stat6 deficient CD4 and CD8 T cells, and c-Maf directly transactivated IL-10 gene expression through binding to a MARE motif in the IL-10 promoter. Together, these data reveal a novel role for c-Maf in regulating T effector development, and suggest that TGFbeta may antagonize Th17 immunity by IL-10 production through c-Maf induction.