Background: Lung cancer is the main cause of cancer death in the world, with small-cell lung cancer (SCLC) accounting for about 10-15% of all lung cancers. Although programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors represent a major breakthrough in SCLC treatment, only a minority of patients will benefit and there is still a lack of accurate biomarkers to guide clinical application. Inflammation plays a crucial role in tumorigenesis, tumor development, metastasis, and drug resistance, but there is limited research on the predictive value of these inflammatory indicators in SCLC. The purpose of our study was to determine the influence of prognostic nutritional index (PNI), systemic immune inflammation (SII), and other indexes on the efficacy and prognosis of patients with SCLC treated with PD-1/PD-L1 inhibitors. Methods: A total of 700 patients of SCLC treated with PD-1/PD-L1 inhibitors in the Fourth Hospital of Hebei Medical University from January 2019 to January 2023 were retrospectively analysed. Among these patients, 246 were included after the inclusion and exclusion criteria were applied. The basic clinical data of patients were collected, included age, sex, PD-1 or PD-L1 inhibitors and so on. The neutrophil:lymphocyte ratio (NLR), platelet:lymphocyte ratio (PLR), PNI, SII, and monocyte:lymphocyte ratio (MLR) were calculated. SPSS 27 software was employed for statistical analysis. As of 1st March 2023, all patients had received a post-diagnosis follow-up. The median follow-up time was 11.7 months. Results: Among the 246 patients with SCLC receiving PD-1/PD-L1 inhibitor treatment. the overall response rate and disease control rate were 47.6% and 89.8%, respectively. Median progression-free survival (PFS) and median overall survival (OS) were 9.0 months and 21.4 months, respectively. Multivariate analysis showed that MLR [hazard ratio (HR) =0.631; P=0.01], and platelet (PLT) count (HR =1.641; P=0.009) were independent risk factors for PFS. NLR (HR =0.566, P=0.01) and lactate dehydrogenase (LDH) (HR =0.446; P=0.002) were independent risk factors for OS. Conclusions: Among patients with SCLC treated with PD-1/PD-L1 inhibitors, those with high MLR and low PLT had shorter PFS, whilst patients with high NLR and LDH had a shorter OS. NLR and LDH may be used as prognostic biomarkers patients with SCLC treated with PD-1/PD-L1 inhibitors. The promising clinical application of NLR and LDH in efficacy prognostic indicators and beneficiary selection for SCLC immunotherapy is highlighted.