Olecranon bursitis rarely Progresses to septic arthritis. In our case, the 24 year old woman was visited due to progressing right elbow pain, despite antibiotic treatment of chronic olecranon bursitis caused by elbow laceration 2 months ago. Pus draining sinus, localized heating and swelling could be seen on physical examination. Septic arthritis and pathologic fracture was diagnosed under arthroscopic examination. Arthroscopic irrigation and synovectomy for elbow joint, olecranon bursectomy and curettage of olecranon bone was done. In the operation field, the elbow and draining sinus over olecranon was communicated each other on saline irrigation test. The patient was treated for 3 weeks with intravenous antibiotics. At postoperative 4 weeks, bone graft was done. The possibility of chronic osteomyelitis and septic arthritis must be considered in a patient with chronic olecranon bursitis.