Background: Rhinosinusitis is one of the most concerning illness due to high medical cost and its negative effect on the respiratory tract. The etiology of chronic rhinosinusitis remains unknown. The main cause of chronic rhinosinusitis with or without nasal polyp is bacterial infections; thus antibiotics remain a main therapeutic intervention. Prescription of broad spectrum antibiotics and the inappropriate combination of antibiotics are the main factors of antibiotic resistance. This study aims to obtain the pattern of aerobic and anaerobic bacteria in chronic rhinosinusitis patient (with or without nasal polyp) and its sensitivity pattern, in Medan, Indonesia. Methods: This is a case series. Samples were patient with chronic rhinosinusitis who had undergone functional endoscopic sinus surgery (FESS). Results: The most common aerobic bacteria found is Klebsiella oxytoca (21.7%), and it is sensitive to ceftriaxone, cefotaxime, levofloxacin, and meropenem. While for the anaerobic bacteria, one patient was positive for Peptostreptococcus and it is sensitive to chloramphenicol. Conclusion: The most common bacteria in the maxilla in patients with chronic Rhinosinusitis with and without polyps in Medan are the aerobic bacteria Klebsiella oxytoca and anaerobic bacteria Peptostreptococcus. It is suggested that the antibiotic prescribed should be based on microbiology examination.