Background: Timely diagnosis of pneumonia in intubated critically ill patients is challenging because the clinical signs and symptoms lack sensitivity and specificity also microbiological identification of organisms may take 48–72 h. Pentraxin 3 (PTX3) is a marker produced at sites of infection and inflammation which can be measured in few hours. Objective: to assess the role of PTX3 as a biomarker in the diagnosis of Ventilator Associated Pneumonia. (VAP). Methodology: This prospective study was conducted on 60 patients, 30 patients were admitted in the Chest Intensive Care Unit (CICU) of Ain Shams University Hospitals suspected to have VAP by modified Clinical Pulmonary Infection Score (CPIS), Level of PTX 3 was measured in serum and Mini Bronchoalveolar Lavage (MiniBAL) using an ELISA, level of C-Reactive Protein (CRP), Complete Blood Picture (CBC) and bacteriological culture were done to diagnose VAP. In 30 healthy controls we measured the serum level of PTX 3. Results: Bacteriologically confirmed VAP was diagnosed in 24 patients, with most common isolated organism was staphylococcus aureus (23%). The Receiver Operating Characteristic (ROC) curve analysis was performed to evaluate the discriminative ability of PTX3 (in serum and MiniBAL) to identify bacteriologically confirmed VAP. For PTX 3 in MiniBAL the Area Under the Curve (AUC) was 0.993 and a cut-off point of ≥3.6 had sensitivity of 95.83% and a specificity of 100.Serum PTX 3 AUC value was 0.826 and cut-off point of 7ng/ml was associated with 62.5% sensitivity, 100% specificity. For CRP, a cut-off level ≥12 mg/dl in serum was associated with 62.5% sensitivity, 83.3% specificity. Conclusion: PTX3 may serve as a useful biomarker in the detection of bacteriologically confirmed VAP patients.