Objective To determine whether there are biologic differences in the Pseudomonas aeruginosa strains isolated from respiratory specimens among the elderly patients with acute exacerbation of chronic obstructive pulmonary disease (COPD) or those with ventilator associated pneumonia (VAP). Methods A total of 48 strains of Pseudomonas aeruginosa isolated from the respiratory specimens of the elderly with acute exacerbation of COPD and VAP who admitted in our department from January 2012 to March 2014 were collected; and among them, 22 were from the COPD patients and 26 from the VAP patients. Biofilm formation was quantified and classified with crystal violet staining. The production of pyocyanin was measured with chloroform extraction method, and the elastase activity was determined with elastin-congo red staining. Results Biofilm formation abilities were similar in the strains isolated from respiratory specimens of COPD group and VAP group (P>0.05), but there existed individual differences. No obvious differences were observed in the production of main virulence factors (pyocyanin and elastase) between the 2 groups (P>0.05). ConclusionPseudomonas aeruginosa strains from the elderly with acute exacerbation of COPD and VAP have similar biofilm formation abilities and production of main virulence factors.