Pseudomonas aeruginosa has been frequently detected from sputa around tracheostomy stuma with a high frequency of nosocomial infection among patients with an opportunistic infection. It is also reported to be difficult to treat lower respiratory infections when resistance to antibiotics for Pseudomonas aeyuginosa has developed. We discuss 15 patients, (8 males and 7 females) who underwent tracheostomy and in whom Pseudomonas aeyuginosa was isolated for 10 years from April 1993 to March 2003. Average age was 62.0 years old. All subjects were oral cancer patients. Pseudomonas aeyuginosa was detected from cultures in 15 of 19 patients (78.9%) . It was isolated from and had colonized the lower respiratory tract by 34.6 days on average after tracheostomy. Gradual change of sensitivity to antiobiotics and increase of drug tolerance were recognized. As drug tolerance may be affected by long-term administration of antibiotics, selection of antibiotics and period should be carefully considered to avoid the development of tolerance.