Moraxella osloensis is a rare causative agent of infection in humans with most cases reported in immunocompromised patients. We report a case of 40years old chronic alcoholic patient who presented with septic arthritis of left knee joint. Culture of pus aspirate was found to be positive for gram negative coccobacilli that were aerobic, oxidase positive and catalase positive. M.osloensis was identified by Biochemical tests and Vitek 2 Compact. Prompt control of infection was achieved by treatment with Meropenem for 7 days along with debridement of left knee joint.