GATA-3 plays a central role in regulating Th1 and Th2 cell differentiation. Upon interleukin (IL)-4 binding to its receptor, GATA-3 is induced through the action of Stat6. GATA-3 regulates Th2 cytokine expression not only at the transcription level, such as directly binding to the promoters of the IL-5 and IL-13 gene, but also by the involvement in the remodeling of the chromatin structure and opening the IL-4 locus. As a master control, GATA-3 stabilizes the Th2 phenotype by two methods. First, GATA-3 shuts down Th1 development through the repression the IL-12 receptor beta2-chain expression. Second, GATA-3 augments its own expression by a positive feedback autoregulation. In this article, we review the recent study of the function of GATA-3 in Th1 and Th2 differentiation.