Regulatory T cells (T reg cells) are essential for self-tolerance and immune homeostasis. Lack of effector T cell (T eff cell) function and gain of suppressive activity by T reg cells are dependent on the transcriptional program induced by Foxp3. Here we report that repression of SATB1, a genome organizer that regulates chromatin structure and gene expression, was crucial for the phenotype and function of T reg cells. Foxp3, acting as a transcriptional repressor, directly suppressed the SATB1 locus and indirectly suppressed it through the induction of microRNAs that bound the SATB1 3ĝ€2 untranslated region. Release of SATB1 from the control of Foxp3 in T reg cells caused loss of suppressive function, establishment of transcriptional T eff cell programs and induction of T eff cell cytokines. Our data support the proposal that inhibition of SATB1-mediated modulation of global chromatin remodeling is pivotal for maintaining T reg cell functionality.