ObjectiveTo explore the value of procalcitonin (PCT) and lipopolysaccharide (LPS) in identifying pathogens and evaluating therapeutic efficacy of hospitalacquired pneumonia (HAP).MethodsA total of 110 HAP patients were enrolled in a prospective study, patients were divided into gramnegative bacterial infected HAP group (G- infected group, n=50), grampositive bacterial infected HAP group (G+ infected group, n=30),and control group (nontypical pathogen or virus infected group, n=30).  Serum levels of PCT, LPS and Creactive protein (CRP) of  patients were dynamically detected, receiver operating characteristic (ROC) curve and area under the curve (AUC) were adopted to assess the value of PCT and LPS in predicting pathogenic bacteria causing HAP.ResultsPCT and LPS levels of G - infected group were （3.43±1.15）ng/mL and （0.20±0.08）EU/mL respectively, which were higher than G+ infected group （［0.42±0.12］ng/mL and ［0.05±0.02］EU/mL respectively）and control group（［0.14±0.08］ ng/mL and ［0.02±0.01］EU/mL respectively)(all P＜0.05). Levels of PCT and CRP of G-  infected group before and after therapy were both significantly different (［3.43±1.15］ ng/mL vs ［0.63±0.22］ng/mL, ［47.26±30.35］ mg/L vs ［9.21±6.54］ mg/L, respectively)(both P＜0.01).The levels of PCT, LPS, and CRP in moderate and severe patients were all significantly higher than mild patients (［5.43±1.05］ng/mL vs ［0.72±0.32］ng/mL, ［0.33±0.07］ EU/mL vs ［0.09±0.04］ EU/mL, ［57.46±20.15］ mg/L vs ［8.25±5.24］ mg/L,respectively)(all P＜0.05）. Sensitivity and specificity of combined detection of PCT and LPS in differentiating gramnegative bacteria infected VAP from grampositive bacteria infected VAP were 95.83% and 96.15% respectively, AUC was 0.95.ConclusionPCT and LPS have certain value in identifying pathogens of HAP, combined  detection of PCT and LPS can increase specificity in identifying HAP type, and assess the efficacy of antimicrobial therapy in accordance with the dynamic change.