Multiple layers of suppressive components including regulatory T (T(Reg)) cells, suppressive antigen-presenting cells, and inhibitory cytokines form suppressive networks in the ovarian cancer microenvironment. It has been demonstrated that as a major suppressive element, T(Reg) cells infiltrate tumor, interact with several types of immune cells, and mediate immune suppression through different molecular and cellular mechanisms. In this paper, we focus on human ovarian cancer and will discuss the nature of T(Reg) cells including their subsets, trafficking, expansion, and function. We will briefly review the development of manipulation of T(Reg) cells in preclinical and clinical settings.