Pseudomonas aeruginosa is an important opportunistic pathogen usually resistant to most antimicrobials. We present changes in the resistance pattern of R aeruginosa to amikacin (AK) and ciprofloxacin (CIP) between January 2002 and June 2004. The physicians of each unit were given information on antibiotic resistance rates of P aeruginosa isolated from ward patients at regular intervals. The antibiotic resistance of 161 P aeruginosa isolates isolated from intensive care units (ICUs) and non-ICUs were tested by disk diffusion method, and the results were interpreted according to the guidelines of National Committee for Clinical Laboratory Standards. Thirty-five percent of all the P aeruginosa isolates were resistant to AK in 2002, 18% in 2003, and 20% in 2004. The CIP resistance rates were 4% in 2002, 26% in 2003 and 20% in 2004. In that period, resistance to AK decreased, whereas resistance to CIP increased. The usage rate of AK in 2002 was 32%, which fell to 26% in 2003 (p<0.05). This rate increased to 27% in 2004 (p<0.05). The usage rate of CIP was very low in 2002 (3%). Subsequently, it increased to 8% in 2003 and 2004 (p<0.05). The changes in resistance rates may have been due to alteration in drug usage policy in our hospital. It is important to provide physicians with information on antibiotic resistance rates at regular intervals to guide therapy for critical P. aeruginosa infections.