Abstract: Objective To explore the value of serum procalcitonin (PCT), interleukin-18 (IL-18) and acute physiology and chronic health evaluation (APACHE) score in prognostic prediction to severe pneumonia in elderly patients. Methods Totally 286 elderly patients with severe pneumonia were selected from January 2013 to October 2016 in Hainan Provincial Hospital of traditional Chinese medicine, and divided into survival group (n=203 cases) and death group (n=83 cases) according to the 28-day survival. The dynamic changes of serum PCT, IL-18 levels and APACHEⅡscore were compared between the two groups at D1, D4 and D7. Multivariate Logistic regression analysis was used to analyze the risk factors of prognosis in elderly patients with severe pneumonia, and the ROC curve was used to evaluate the predictive value of PCT, IL-18 and APACHEⅡscore in the prognosis of elderly patients with severe pneumonia. Correlation analysis of PCT with IL-18 and APACHE was performed by Pearson correlation analysis. Results The serum PCT(4.69±1.75) ng/ml vs (0.41±0.15) ng/ml, IL-18 (85.16±20.17) ng/ml vs (68.23±18.56) ng/ml and APACHEⅡscore (27.84±4.63) ng/ml vs (23.87±4.16) ng/ml in the death group were significantly higher than those in the survival group (P< 0.05, respectively). Logistic regression analysis showed that mechanical ventilationOR(95% CI):6.018 (2.175-11.974), PCTOR(95% CI):2.427 (1.359-5.826), IL-18OR(95% CI):1.805 (1.106-4.283) and APACHE scoreOR(95% CI):4.482 (1.892 -8.747) were independent risk factors of death in elderly patients with severe pneumonia (P< 0.05, respectively). ROC curve showed that combination of PCT,IL-18 and APACHEⅡscore was most sensitive (89.4%) and specific (81.6%) for predicting mortality in elderly patients with severe pneumonia. Correlation analysis showed that the serum PCT level in death group was positively correlated with IL-18 and APACHE score (r=0.473, P=0.025; r=0.681, P< 0.001). Conclusion Serum PCT, IL-18and APACHEⅡscore are independent risk factors for mortality in elderly patients with severe pneumonia, and combination of three indexes is of good value in predicting the prognosis.