Background: The moment most common cause of in-hospital infection is pneumonia. Pneumonia is prevalent within the ICU (Intensive Care Unit) setting and can be deadly. The Incidence of pneumonia is approximately 17% in the therapeutic ICU2 but can be 6 to 20 times increased in mechanically ventilated patients. The duration of hospital stay and expenditure are both expanded in patients who develop ventilator-associated pneumonia. This study aims to identify the causative microorganism responsible for CAP (Community-Acquired Pneumonia) and VAP (Ventilator-Associated Pneumonia) and their antibiotic sensitivity pattern. Methods: This was a comparative cross-sectional study that was carried out at two ICU in Sylhet city. The data was collected from the patient's medical information, the patient's file, and the hospital information system. Culture and sensitivity (C/S) were collected from the electronic medical information system (MIS). All data from January 2019 to December 2020, including patient's information, course of the disease (in terms of death or recovery-if available), clinical features, and investigation reports, was transferred to an electronic data collection sheet (Microsoft Excel). After completion of all data collection, analysis was conducted through a spreadsheet. Comparison between two disease groups was made by independent t-test. Within the group, the analysis was done by the Chi-Square test. Results: In this thesis study, it was found that the most common organism responsible for CAP was Streptococcus spp. (34.70%) and is sensitive to Meropenem (92.21%), Imipenem (88.16%), Amikacin (70.67%), Piperacillin (70.91%), Moxifloxacin (70.96%), Levofloxacin (67.95%), Amoxiclav (67.92%), and Ceftriaxone(63.95%). The most common causative organism responsible for VAP was Staphylococcus spp. (36.51%) and it was sensitive to Imipenem (100%), Moxifloxacin (100%), Meropenem (94.73%), Amikacin (85.71%), Ceftriaxone (60%), Amoxiclav (66.66%), Levofloxacin (57.14%), and Cefuroxime (50%). Conclusion: Pneumonia is still one of the most common reasons for hospitalization, particularly for those admitted to ICU. It has been observed in several studies that the majority of the cases are communityacquired pneumonia. Many mechanically ventilated patients often develop VAP, which is fatal if timely diagnosis and appropriate antibiotics administration are not made. Streptococcus spp. was the most common organism responsible for CAP, and Staphylococcus spp. mainly was responsible for VAP.