Abstract: Programmed cell death protein-1 (PD1) and programmed cell death protein-1 ligand 1 (PD-L1) act as important negative immune regulators. Combining PD1 receptors on T cells with their corresponding ligands PD-L1 on tumor cells can inhibit T cell activation and lead to tumor cell immune escape and resistance to conventional chemotherapy. In recent years, the drugs targeting PD1/PD-L1 monoclonal antibodies have achieved promising effects in various tumor types including non-small cell lung carcinoma and melanoma. They also dramatically improved poor prognosis and overall survival of some tumor patients. In this review, we will summerize the novel findings on the activation of PD1/PD-L1 in tumor occurrence, development and metastasis, as well as the updated clinical progress of using anti-PD1 or anti-PD-L1 in tumor immunotherapy.