Pulmonary pleomorphic carcinoma has been shown to respond remarkably to PD-1 inhibitors; however, the biomarkers for this therapy have not been fully proven. We report a case of pulmonary pleomorphic carcinoma with overexpressed PD-L1, in which a complete response to nivolumab was sustained for >14 months. Immunohistochemical analysis revealed few PD-1+ immune cells and regulatory T cells in the tumor, in addition to predominant infiltration of CD8+ cells and macrophages. Our findings suggest that the presence of a small number of PD-1+ immune cells and regulatory T cells should be investigated as candidate therapeutic biomarkers.