Objective To assess the value of procalcitonin ( PCT) in serum and percentage of infected cells ( PIC) in bronchoalveolar lavage fluid ( BALF) for the diagnosis of early ventilator-associatedpneumonia ( VAP) .Methods A prospective observational study was conducted in a teaching hospital. The patients consecutively admitted to the intensive care unit from January 2011 to June 2012, who received mechanical ventilation for more than 48h and clinically suspected for VAP, were recruited in the study.Patients with infection outside the lungs and previous diagnosed infection were excluded. PCT was detected and bronchoalveolar lavage was performed in the day when VAP was diagnosed. BALF cells were stained by May-Grunwald Giemsa ( MGG) for counting 100 phagocytic cells and calculating infected cells ( ICs )percentage.Results 76 of all 421 patients were enrolled in this study, 64 of which were diagnosed, 12 were under-diagnosed. The PCT [ ( 3. 48 ±1. 46) ng/mL vs. ( 1. 53 ±0. 60) ng/mL] and PIC [ ( 3. 11 ±1. 47) % vs. ( 1. 08 ±0. 29) % ] were significant higher in the patients with VAP. The threshold of 2 ng/mL of PCT and 2% of PIC corresponded to sensitivity of 78. 12% and 78. 12% , and specificity of 75. 00% and 91. 67% , respectively. The area under the receiver operating characteristic ( ROC) curve was 0. 87 ( 95% CI 78. 9%-95. 9% ) and 0. 874 ( 95% CI 79. 2% -94. 9% ) , respectively. The area under ROC curve was 0. 979, and the sensitivity was 97. 36% , specificity was 97. 36% when the two cutoff values were both achieved. Conclusion PCT and PIC are useful markers to diagnose early VAP quickly and conveniently and allow early antibiotic treatment of patients with suspected VAP.