Objective: This study was aimed to evaluate the correlation between inflammatory markers [neutrophil / lymphocyte ratio (NLR), platelet / lymphocyte ratio (PLR), monocyte / lymphocyte ratio (MLR) and systemic immune-inflammation index (SII)] and 18F-fluorodeoxyglucose (FDG) positron emission tomography / computed tomography (PET/CT) metabolic parameters [maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), metabolic tumor volume (MTV), TLG (total lesion glycolysis)] in patients with small cell lung cancer (SCLC) at baseline. Methods: A total of 56 patients who undergone 18F-FDG PET/CT and did not receive any treatment in Department of Nuclear Medicine, the First Affiliated Hospital of Nanjing Medical University between 2014 and 2019 were analyzed retrospectively. The metabolic parameters of primary tumor, clinical data and inflammatory markers (neutrophil count, monocyte count, lymphocyte count, platelet count) within one week before PET/CT detection were collected to analyze the correlation by Spearman’s rho test. Results: The slight positive correlations were found between inflammatory markers (NLR, PLR, MLR, SII) and partial metabolic parameters [TLG (rNLR=0.309, rPLR=0.304, rMLR=0.271, rSII=0.362), MTV (rNLR=0.354, rPLR=0.341, rMLR=0.290, rSII=0.411)] of primary tumor in 56 patients with SCLC (all P＜0.05). The SUVmax and SUVmean were not found the correlation with these hematological parameters (all P＞0.05). The NLR, MLR, SII, neutrophils, MTV and TLG in extended stage were higher than those in limited stage, and the lymphocytes in extended stage were lower than those in limited stage(all P＜0.05), but SUVmax, SUVmean, PLR, monocytes and platelets were not found differences in extended and limited stage(all P＞0.05). Conclusion: Baseline inflammatory markers of SCLC not only reflect the systemic metabolism, but also reflect the local inflammation of tumor. And it might be necessity to undergoing Whole-body PET/CT for staging and adjusting treatment strategy in those patients with high NLR, MLR or SII.