MicroRNAs (miRNAs)-mediated RNA interference are emerging as an important regulatory pathway for various biological processes, including development, differentiation, and homeostasis. Accumulated evidence suggests that miRNAs regulate T cell and B cell differentiation, proliferation, and apoptosis. Deletion of miRNAs in hematopoietic stem cells or in thymus disrupts T cell homeostasis and results in autoimmunity and abnormal cytokine production. Regulatory T cells are potent immune regulators. In this mini-review, we provide a brief overview of the important roles of miRNAs in the development and function of T cells, especially in immune regulatory T cells.