Olsenella uli is a Gram-positive bacterium common in the oral cavity or gastrointestinal tract. Here we reported a first case of human pneumonia caused by the Olsenella uli. The identification of Olsenella uli was based on micromorphology, sequence analysis and mass spectrometry analysis of the bacteria recovered from sputum. Ceftazidime，one of the third generation cephalosporins was used for the anti-infection treatment of the patient. CT results showed a significant improvement of the pulmonary lesion and pleural effusion and recovery from pulmonary infection after 10 days. The mechanism underlying Olsenella uli induced pneumonia is unclear, our report suggests a causative role of gingival bacteria in pathogenesis of pneumonia, and the intervention by Ceftazidime may offer a therapeutic strategy for Olsenella uli infection.