Abstract： Objective To investigate the distribution and antimicrobial resistance of pathogens isolated from lower respiratory tracts of early onset and late-onset ventilator-associated pneumonia (VAP)patients in intensive care unit. Methods A retrospective analysis was performed on data collected from1324 patients admitted to the ICU in the Third People' s Hospital in Wenzhou from July 2008 to December 2011 who received invasive mechanical ventilation.Patients were divided into early-onset pneumonia group (EOP,≤ 4 d mechanical ventilation ) and late-onset pneumonia group (LOP, ＞ 4 d mechanical ventilation).x2 or t test was performed to compare the pathogen distribution and antimicrobial resistance between two groups.Results In 1324 patients,552 (41.7％) suffered from VAP,including 74 ( 5.6％ )patients with EOP,382 (28.9％) patients with LOP,and 96 (7.3％) patients with both EOP and LOP.The top 6 pathogens in EOP group were Acinetobacter baumannii ( 72,22.6％ ),Pseudomonas aeruginosa (45,14.1％ ),Klebsiella pneumoniae (32,10.0％ ),Canidia albicans ( 31,9.7％ ),Burkholderia cepacia ( 31,9.7％ ) and Staphyloccocus aureus ( 28,8.8％ ) ; and in LOP group were Acinetobacter baumannii (235,21.2％ ),Canidia albicans (201,18.1％ ),Pseudomonas aeruginosa ( 111,10.0％ ),Candida glabrata ( 86,7.8％ ),Klebsiella pneumoniae ( 81,7.3％ ) and Staphyloccocus aureus ( 46,4.2％ ).Staphylococcus aureus infection in EOP group was more common than that in the LOP group (x2 =10.780,P =0.002),but the separation rate of Candida albicans in EOP group was significantly lower than that in the LOP group (x2 =12.907,P =0.000).Gram-negative bacteria isolated from EOP or LOP group were both highly resistant to most commonly used antibacterial agents,especially for Acinetobacter baumannii and Pseudomonas aeruginosa strains. Most Staphyloccocus aureus strains were methicillin-resistant strains (EOP:67.9％,19/28; LOP:63.0％,29/46).Canidia albicans and Candida glabrata were sensitive to most antifungal agents.Conclusion For both EOP and LOP groups,the majority of pathogens isolated from lower respiratory tract are Gram-negative bacteria,and drug resistance is serious.