Increased Antimicrobial resistance among clinically important Gram-negative bacilli, especially Carbapenemase-producing Enterobacterales and Pseudomonas, has regained interest in Polymyxin E (Colistin) and Polymyxin B as a last resort of treatment. Broth micro-dilution (BMD) is Colistin's only recommended susceptibility testing, but this method is impractical for most clinical laboratories. Aims & Objectives: The study aims to evaluate the accuracy of the Colistin Broth Disk Elution test (CBDE) and the Broth Micro Dilution (BMD) method in obtaining Colistin MIC for Carbapenem-resistant Gram-negative bacilli (CRGNB) among all clinical isolates. Materials & Methods: A Cross-sectional descriptive study was conducted in the Department of Microbiology, NRIIMS, Vizag, from September 2022 to February 2023. During this period, 1496 clinical samples (including Blood, Purulent exudates, ET aspirates, and sterile body fluids) were collected by convenient sampling and processed. All Gram-negative bacilli isolates obtained from all age groups were included in our study. Repeated isolates from the same patient, isolates from stool samples and the organisms which are intrinsically resistant to Colistin, such as Proteus, Serratia, Providencia and Burkholderia species, were excluded from the study.