Pulmonary sarcomatoid carcinoma is characterized by poor survival rates compared with other non-small cell lung cancer. Prognostic nutritional index has significant prognostic value in many malignant tumors. We conducted this retrospective study to investigate the role of prognostic nutritional index in patients with pulmonary sarcomatoid carcinoma and to determine prognostic factors. Of 8176 patients with resected lung cancer in a single high-volume institution between 2008 and 2015, 91 patients with pathologically diagnosed sarcomatoid carcinoma were included in our study and evaluated. Kaplan-Meier analysis and Cox regression analysis were conducted to analyze clinicopathologic data. Subgroup analysis of overall survival (OS) and recurrence-free survival (RFS) among pulmonary sarcomatoid carcinoma patients were also conducted. Univariable analysis showed that tumor size (P = 0.018 in OS), and P = 0.021 in RFS), tumor stage(P < 0.001 in OS, and P = 0.002 in RFS), nodal metastasis (P < 0.001 in OS, and P < 0.001 in RFS), pathological stage (P < 0.001 in OS, and P < 0.001 in RFS), treatment modality (P = 0.032 in OS, and P = 0.059 in RFS) and PNI (P < 0.001 in OS, and P < 0.001 in RFS), were significant factors of both OS and RFS. In multivariable analysis, for OS, the pathological stage (Hazard ratio (HR) 1.432; 95% confidence interval (95% CI) 1.210-1.695; P < 0.001) and PNI (HR 0.812; 95% CI 0.761-0.865; P < 0.001) were independent prognostic factors. And for RFS, We found PNI as an independent prognostic factor (HR 0.792; 95% CI 0.739-0.848; P < 0.001), and the pathological stage (HR 1.373; 95% CI 1.160-1.625; P < 0.001). In the subgroup of patients with PNI ≥ 49.4, univariable analysis showed treatment modality was a significant factor of overall survival (P = 0.001); multivariable analysis showed patients received postoperative chemotherapy (HR 0.288; 95% CI 0.095-0.874; P = 0.028) or postoperative chemotherapy with targeted therapy (HR 0.148; 95% CI 0.030-0.726; P = 0.019) has better overall survival rates. The PNI and the pathological TNM stage are independent prognostic factors for pulmonary sarcomatoid carcinoma. PNI is an important indicator for the selection of postoperative adjuvant therapy. Patients with PNI ≥ 49.4 may benefit from postoperative chemotherapy and targeted therapy. We still need further prospective studies to confirm these results.