The complement system represents an innate immune response consisting of a protein network. Over-activation of the complement system plays an important role in inflammation, tissue damage, and infectious disease severity. The prevalence of MERS-CoV in Saudi Arabia remains significant and cases are still being reported. The role of complement in Middle East Respiratory Syndrome coronavirus (MERS-CoV) pathogenesis and complement‐modulating treatment strategies has received limited attention, and studies involving MERS-CoV-infected patients have not been reported. This study offers the first insight into the pulmonary expression profile including Seven complement proteins including complement regulatory factors during MERS-CoV infection. We also measured the expression of lung neutrophil chemoattractant chemokine IL-8 (CXCL8) and RANTES (CCL5). Our results significantly indicate high expression levels of complement anaphylatoxins (C3a and C5a), IL-8, and RANTES in the lungs of MERS-CoV-infected patients. The upregulation of lung complement anaphylatoxins, C5a and C3a, was positively correlated with IL-8, RANTES and the fatality rate. Our results also showed upregulation of the positive regulatory complement factor P (properdin), suggesting positive regulation of the complement during MERS-CoV infection. In addition, we also demonstrated that a high viral load in all patients with MERS-CoV correlated with C5a and C3a levels. Pulmonary complement mediators, disease severity, and an increased fatality rate may be linked to the degree of complement activation against MERS-CoV. High levels of lung C5a, C3a, factor P, IL-8 and RANTES may contribute to the immunopathology, disease severity, ARDS development, and a higher fatality rate in MERS-CoV-infected patients. These findings highlight the potential prognostic utility of C5a, C3a, IL-8 and RANTES as biomarkers for MERS-CoV disease severity and mortality. To further explore the functional partners (protiens) prediction of highly expressed proteins (C5a, C3a, factor P, IL-8 and RANTES), the computational protein–protein interaction (PPI) network was constructed, and six proteins (hub nodes) were identified.