Objective:To explore the value of peripheral blood ionized calcium on the prognosis of elderly patients with sepsis.Methods:The clinical data of 73 elderly patients with sepsis from January 2018 to June 2019 in Shanghai Minhang Hospital, Fudan University, were retrospectively analyzed. Among them, 19 patients died within 28 days (death group), and 54 patients survived (survival group). The peripheral blood ionized calcium, procalcitonin (PCT), acute physiology and chronic health evaluation Ⅱ (APACHE Ⅱ) and arterial lactic acid were compared between 2 groups. The risk factors affecting prognosis in elderly patients with sepsis was analyzed by multivariate Logistic regression. The receiver operating characteristic (ROC) curve was used to analyze the ability of each indicator in evaluating the prognosis.Results:The peripheral blood ionized calcium in death group was significantly lower than that in survival group: (0.93 ± 0.07) mmol/L vs. (1.05 ± 0.16) mmol/L, the PCT and APACHE Ⅱ were significantly higher than those in survival group: 2.43 (1.89, 3.76) μg/L vs. 1.34 (1.05, 2.72) μg/L and (20.20 ± 2.86) scores vs. (17.40 ± 3.95) scores, and there were statistical differences ( P<0.01); there was no statistical difference in arterial lactic acid between 2 groups ( P>0.05). Multivariate Logistic regression analysis result showed that the peripheral blood ionized calcium and PCT were independent risk factors affecting the prognosis in elderly patients with sepsis ( OR = 1.634 and 1.876, P<0.05). The ROC curve analysis result showed that the area under curve (AUC) of peripheral blood ionized calcium for the prognosis in elderly patients with sepsis was 0.844 (95% CI 0.740 to 0.918), the optimal cut -off value was 0.89 mmol/L, with a sensitivity of 83.3% and a specificity of 79.0%; the AUC of PCT for the prognosis in elderly patients with sepsis was 0.880 (95% CI 0.783 to 0.944), the optimal cut -off value was 2.79 μg/L, with a sensitivity of 81.4% and a specificity of 89.5%. Conclusions:The level of peripheral blood ionized calcium can predict the clinical outcome of elderly patients with sepsis.