Cancer derives from mutant oncogenic cells, which tend to thrive within immunocompromised individuals. As the basic research on cancer goes deeper, the knowledge of the existence of a variety of antitumor components is gradually revealed. Cells including NK cells, dendritic cells, B cells and T cells, and their associated immune molecules such as cytokines, ligands and antibodies, all showed particular anti-tumor effects. At the same time, immunosuppressive cells such as regular T cells, tumor associated macrophages, regulatory DCs and myeloid derived suppressive cells, and their corresponding secretory factors were revealed to suppress anti-tumor effects. These basic research findings suggest that harnessing the immune system in the right ways might control cancer.