Abstract: Objective：To investigate the correlation of adult community-acquired pneumonia (CAP) severity with lactate dehydrogenase (LDH) and serum amyloid protein A (SAA). Methods：A total of 100 patients with CAP in our hospital from Nov. 2017 to Oct. 2018 were selected. Clinical characteristics including gender, age, personal medical history, body mass index (BMI) were recorded, blood pressure, heart rate, number of breaths per minute were measured, the state of consciousness, chest CT, blood gas analysis, routine blood test, urea nitrogen, procalcitonin (PCT), C reactive protein (CRP), LDH, SAA examinations were performed. According to their condition, the patients were divided into common pneumonia group (n=62) and severe pneumonia group (n=38). Differences in patients’ parameters between the two groups, and the relationship between various parameters and the severity of pneumonia was analyzed. Results：White blood cell (WBC), PCT, CRP, LDH, and SAA in common pneumonia group is lower than those in severe pneumonia group (P＜0.05). Logistic regression analysis showed that LDH and SAA were correlated with the severity of the disease （P＜0.05）. Receiver-operating characteristic (ROC) analysis showed that area under the curve (AUC) of LDH was 0.894, the cut-off point was 228.5 U/L, with a sensitivity of 81.6%, and a specificity of 87.1%, the Youden index was 0.687 （95%CI 0.819-0.969, P=0.000）. The AUC of SAA was 0.802, the cut-off point was 170 mg/L, with a sensitivity of 84.2%, and a specificity of 85.5%, the Youden index was 0.697 (95%CI 0.714-0.889, P=000). Conclusions：LDH and SAA might be related to the severity of CAP, and they have the potential to be used to reflect the severity of CAP.