OBJECTIVE To study the isolation and resistance tendency of Acinetobacter calcoaceticus-baumannii to antimicrobial agents from 1998 to 2004 to provide valuable data for infection prevention and therapy. METHODS We reviewed the isolation rates,distribution in clinical specimens and wards,and the resistance rates of(A.calcoaceticus-baumannii)to 14 kinds of antimicrobial agents from 1998 to 2004. RESULTS There was an increasing tendency of isolation rates of A.calcoaceticus-baumannii every year,which was 0.18% in 1998 but 1.48% in 2004.In the seven years,there was the highest isolation rate of 70.58% in specimens from respiratory tract,the next was from the urine(9.42%),and blood(4.63%).Concerning the wards distribution,ICU had the highest rate of 47.28%.In 1998,A.calcoaceticus-baumannii had resistance rates more than 50% only to one kind of antimicrobial agents(aztreonam),but in 2004,it had increased to thirteen kinds(except cefoperazone/sulbactam).About the fourteen kinds of antimicrobial agents we inspected,that were increased in their resistance rate.The highest increasing of resistance rate was ceftazidime from 11.1% in 1998 to 88.9% in 2004,the imipenem was second for 0.0% to 64.8%,and the third was sulfamethoxazole/trimethoprim form 0.0% to 64.0%,while there still was an increasing resistance tendency to them. CONCLUSIONS The clinical isolation rate of A.calcoaceticus-baumannii is increasing,and it has higher resistance rates to many antimicrobial agents as well as an increasing resistance tendency to relatively susceptive antimicrobial agents every year.So physicians should prescribe on the basis of antimicrobial agents susceptibility tests in vitro.