Objective To explore the distribution of bacteria among community acquired lower respiratory tract infection (LRTI) inpatients with underlying chronic respiratory tract diseases.Methods The clinical data，sputum culture and drug susceptibility results of 212 community acquired LRTI patients who were hospitalized during the period 2001-2005 were retrospectively analyzed.All patients had various underlying chronic respiratory tract diseases.Results A total of 229 strains of pathogens were detected，with the majority being gram negative bacteria.In pathogens of acute exacerbation of chronic obstructive pulmonary disease，gram negative bacteria occupied 73.9%.And Pseudomonas aeruginosa and Klebsiella pneumoniae were the most common pathogens，with each occupying 18.2% and 13.6% respectively.Gram positive bacteria occupied 23.8%，mainly Staphylococcus aureus (10.2%) and Streptococcus pneumoniae (9.1%).In patients with bronchiectasis exacerbated by bacterial infection，86.2% were caused by gram negative bacteria，the top three being，in descending order，Pseudomonas aeruginosa (27.5%)，Haemophilus parainfluenzae (13.7%)，and Haemophilus influenzae (11.8%).Bronchiectasis was the major risk factor of getting Pseudomonas aeruginosa infection (OR=5.590，95%CI 2.792~11.192).The risk factors of getting Acinetobacter baumanii infection were antacid usage within 1 month (OR=9.652，95%CI 2.792~11.192) and hypoalbuminemia (OR=2.679，95%CI 1.108~6.476).For enterobacters infections，including Klebsiella pneumoniae，Enterobacter cloacae and Escherichia coli，the risk factors were antibiotic usage within 1 month (OR=4.236，95%CI 1.982~9.057)，having renal diseases (OR=4.305，95%CI 1.090~17.008) and diabetes mellitus (OR=2.836，95%CI 1.339~6.009).Conclusions Gram negative bacteria were the main pathogens of community acquired LRTI in hospitalized patients with underlying chronic respiratory tract diseases.The pathogens were influenced by underlying diseases，severity of diseases and drug usage history of patients.