We investigated the role of Smad4, a signaling molecule of the TGF-beta pathway, in T cells on the pathology of Sjogren's syndrome (SS) in nonobese diabetic (NOD) mice, an animal model of SS. T cell-specific Smad4-deleted (Smad4(fl/fl,CD4-Cre); Smad4 tKO) NOD mice had accelerated development of SS compared with wildtype (Smad4(+/+,CD4-Cre); WT) NOD mice, including increased lymphocyte infiltration into exocrine glands, decreased tear and saliva production, and increased levels of autoantibodies at 12 weeks of age. Activated/memory T cells and cytokine (IFN-Y, IL-17)- producing T cells were increased in Smad4 tKO NOD mice, however the proportion and function of regulatory T (Treg) cells were not different between Smad4 tKO and WT NOD mice. Effector T (Teff) cells from Smad4 tKO NOD mice were less sensitive than WT Teff cells to suppression by Treg cells. Th17 differentiation capability of Teff cells was similar between Smad4 tKO and WT NOD mice, but IL-17 expression was increased under inducible Treg skewing conditions in T cells from Smad4 tKO NOD mice. Our results demonstrate that disruption of the Smad4 pathway in T cells of NOD mice increases Teff cell activation resulting in upregulation of Th17 cells, indicating that Smad4 in T cells has a protective role in the development of SS in NOD mice.