Introduction: Based on previous studies, Plasma total sialic acid (TSA) of many diseases is known as an inflammatory marker.This study attempts to determine TSA levels in patients with pneumonia and introduce it as a perfect diagnostic marker for pneumonia. Materials & Methods: In this study, 30 patients with pneumonia and 20 healthy controls participated. Plasma TSA values were estimated by Sydows method and Data were compared using t-test and ROC curve. Findings: Plasma levels of this marker showed a significant increase in the patient group compared to the control group (p<0.0001). There was a significant positive correlation between TSA concentration and age in patients (p<0.0001, r= 0.718). Area under ROC curve (AUC), diagnostic sensitivity and specificity of total sialic acid for detection of pneumonia were 1, 96.7 and 100%, respectively. Discussion & Conclusions: According to the results, TSA has good sensitivity and specificity for the diagnosis of pneumonia and it can be used as a perfect diagnostic biomarker for this disease.