Abstract: Smallcell lung cancer（SCLC）is characterized by its rapid growth and early development of widespread metastases. Although patients with SCLC are highly responsive to chemotherapy and radiation therapy， longterm prognosis remains poor， with relapse and disease metastasis occurring in almost all cases. Immune checkpoint blockade， especially blockade of programmed death-1（PD-1）receptor and its ligand PD-L1， achieved robust responses and improved survival for patients with SCLC in preclinical and clinical studies. The blockade of PD-1／PD-L1 pathway as a novel therapeutic approach may change the treatment paradigm of SCLC in the future. Data on clinical activity by programmed cell death-1 ligand expression in SCLC are not widely available. In addition， limited data indicate that PD-L1 expression may be an ideal biomarker for patient selection. Here， we summarize the brief history of PD-L1 as a biomarker and describe the critical role of PD-1／PD-L1 inhibitors in SCLC.