Streptococcus anginosus is a member of Streptococcus milleri group, and is found in the oral mucosa, respiratory tract, and gastrointestinal tract as normal flora. It can develop into a disease in patients with deteriorating clinical condition or with clinical risk factors. A previously healthy 15-year-old boy was admitted due to fever, abdominal discomfort and vomiting which lasted for 7 days. He had a history of dental procedure 1 day before the development of fever. He was diagnosed with acute acalculous cholecystitis based on the clinical, laboratory, and imaging finding, and S. anginosus was isolated from the blood culture. The patient was successfully treated with antibiotic therapy.