Acute respiratory distress syndrome (ARDS) is a severe disease with high mortality, and its primary cause is sepsis. The aim of this study was to detect and evaluate the role of Human epididymis protein 4 (HE4) in sepsis-related ARDS. One hundred and twenty-three critically ill sepsis patients with/without ARDS and 102 healthy controls were enrolled in this study. Blood samples were collected upon admission for quantitative testing of HE4 by chemiluminescent microparticle immunoassay (CMIA). ROC curve analysis and Spearman's correlation analysis were conducted to determine the diagnostic and prognostic value of HE4. Compared with controls, the serum HE4 concentrations of sepsis patients were elevated, and levels in sepsis patients with ARDS were significantly higher (all p < 0.0001). Moreover, HE4 concentrations were strongly correlated with the clinical severity characteristics of sepsis patients, and ROC curve suggested that the AUC of HE4 applied to discriminate sepsis-ARDS patients from sepsis patients was 0.903. HE4 was also found to be a prognostic biomarker of clinical severity and 28-day mortality among critically ill sepsis patients. Logistic regression analysis showed that HE4 was an independent factor for diagnosis of ARDS. Meanwhile, ROC curve analysis showed that the cut-off value of serum HE4 to discriminate 28-day mortality from sepsis patients (AUC: 0.782) was 646.5pmol/L. The concentration of serum HE4 in patients with sepsis-related ARDS was markedly increased and was significantly correlated with mortality, which suggests that serum HE4 could be a promising diagnostic and prognostic biomarker for ARDS in sepsis patients.