ObjectiveTo investigate the distribution, antimicrobial susceptibility of Acinetobacter in lower respiratory infection and the association with lung underlying diseases. MethodsAcinetobacter isolated from sputum in patients  from January 2003 to December 2006 were analyzed retrospectively,clinical records were also reviewed and made statistical analysis. ResultsOne hundred and thirtytwo strains of  Acinetobacter strains were isolated, which accounting for 12.70% of total isolated bacteria and 15.02% of gramnegative bacilli, 79 of 132（59.85％）strains were  Acinetobacter baumanii，112(84.85%) strains  of Acinetobacter were isolated from patients with lung underlying diseases. Antimicrobial susceptibility results suggested that isolated Acinetobacter strains were sensitive to meropenem ，cefoperazone/ sulbactam and levofloxacin,  but resistant to aztreonam, mezlocillin and so on. Antimicrobial susceptibility between 79 strains of Acinetobacter baumanii and 53 strains of the other species of Acinetobacter was significantly different（P＜0.05 or P＜0.01）. The sensitive rates to cefoperazone and cefoperazone / sulbactam in 110 Acinetobacter isolates was 51.82% and 83.64% respectively, there was significant difference between  the two (χ2=25.47，P<0.01). Antimicrobial susceptibility test  results between  Acinetobacter isolated from  patients with  respirators and without respirators were also significantly different（P＜0.05 or P＜0.01）. Among 103 patients who were isolated Acinetobacter, 80 patients’ sputum sample delivery time were within 4 days after admission, 23 were 4 days later of admission, antimicrobial susceptibility between two groups was significantly different（t=3.84, P＜0.05）.ConclusionAcinetobacter is the main pathogen in lower respiratory  tract  infection, most of which  is Acinetobacter baumanii; drugresistance of Acinetobacter is serious and related to the use of respirator, time from admission to delivering sputum samples and lung underlying diseases. Acinetobacter is not only the main pathogen in nosocomial  infection, but also can cause  patients with lung underlying diseases develop  communityacquired pneumonia.