Regulatory T cells (Tregs), a fraction of CD4+ T cells with immunosuppressive characteristics, are strongly linked to a number of inflammatory and autoimmune disorders. Furthermore, it also contributes to the development of tumors. Tregs infiltrate into the tumor microenvironment (TME), dampen the anti-tumor immune reaction, and facilitate tumoral immune escape. Besides the well-known hemostatic roles, mounting evidence indicates that platelets may also function as immune cells and engage in cancer immune escape. In addition, substantial evidence shows that platelets or platelet-derived mediators can regulate the proliferation, differentiation, and functions of many immune cells. Platelets also play important roles in promoting tumor cell proliferation and helping tumor cells evade immune surveillance. Here we summarize the regulatory effects of platelets in Treg proliferation, differentiation and functions and highlight the potential synergistic roles of platelets and Tregs in tumor cell immune escape.