Infections caused by multi drug-resistant gram-negative bacilli are increasingly reported worldwide. Colistin, tigecycline and aminoglycosides are almost the only and last choice antibiotics in the treatment of infections caused by carbapenem-resistant Enterobacterales members. Ceftazidime-avibactam is a novel antibiotic combination consisting of a broad-spectrum cephalosporin and avibactam with good antimicrobial activity against carbapenem-resistant Enterobacterales members. The aim of this study was to assess the in vitro activity of ceftazidime-avibactam and colistin against carbapenem-resistant Klebsiella pneumoniae isolates and to obtain local antimicrobial surveillance data. A total of 150 carbapenem-resistant K.pneumoniae isolates obtained from various clinical samples of the patients hospitalized in our hospital between 2018-2021 were included in the study. Duplicate isolates were excluded from the study. The isolates were recovered from blood (n= 72), tracheal aspirate (n= 40), wound (n= 20), biopsy and abscess (n= 10), steril body fluid (n= 5), and peripheral venous catheter (n= 3) samples. Isolates were identified by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS, Bruker Daltonics, Germany). The minimum inhibitory concentration (MIC) values of the isolates for meropenem, colistin, ceftazidime, and ceftazidime-avibactam were determined by broth microdilution method. Susceptibility of the isolates to the tested antibiotics was evaluated by the European Committee of Antimicrobial Susceptibility Testing (EUCAST) criteria. The presence of carbapenemases (VIM, IMP, NDM, KPC, and OXA-48) was investigated by polymerase chain reaction (PCR) using specific primers. The mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5 genes were evaluated by PCR for plasmid-mediated colistin resistance. All K.pneumoniae isolates were found to be positive for at least one of the carbapenemase genes evaluated in the study. The blaOXA-48 gene was detected in 107 (71.3%), blaKPC gene in 25 (16.7%); blaNDM gene in 7 (4.7%), co-production of blaOXA-48 and blaKPC genes in 10 (6.7%), co-production of blaOXA-48 and blaNDM genes in 1 (0.6%) isolate. None of the isolates harbored the blaVIM and blaIMP genes. None of the mcr genes screened in the study were detected among the isolates. The susceptibility of the isolates to ceftazidime-avibactam and colistin was 92.7% (139/150) and 48% (72/150), respectively. The MIC50 and MIC90 values for meropenem, ceftazidime, ceftazidime-avibactam, and colistin of the isolates were determined as 32/256, > 128/> 128, 1/8, and 4/16 µg/ml, respectively. Of the ceftazidimeavibactam resistant isolates, seven were positive for blaNDM, three for blaKPC, and one for both blaOXA-48 and blaNDM genes. High ceftazidime-avibactam MIC levels (> 128 µg/ml) were detected in metallo-betalactamase producing isolates. Consequently, our data suggested that ceftazidime-avibactam exhibited as a good alternative therapeutic choice for carbapenem-resistant K.pneumoniae isolates. It is noteworthy that high rate of colistin resistance was detected in K.pneumoniae isolates. Another notable finding of this study is the increase in K.pneumoniae isolates producing blaKPC for our country. To prevent the development of resistance which is observed even in last-choice therapeutic antibiotics, the principles of rational antibiotic use should be followed. The appropriate antimicrobial susceptibility testing should be routinely performed for surveillance of ceftazidime-avibactam and colistin.