In empyema, the pH of the pleural fluid usually decreases depending on the type of bacterial infection. However, there have been a few case reports of elevated pleural fluid pH. We report a case of empyema with a pleural fluid pH of 8.0. A 71-year-old man presented with chest pain on his right side and was diagnosed with acute pleurisy. Despite the administration of antibiotics, the inflammatory response did not improve and the pleural effusion worsened; the patient was therefore referred to our hospital. A pleural fluid test performed by the previous physician had revealed a pH of 8.0. Because there were many adhesions in the pleural cavity and he had a high inflammatory response in blood tests, we determined that his condition could not be improved by thoracic drainage. Therefore, thoracoscopic resection of right pleural empyema was performed. Intraoperative pleural fluid samples revealed a pH of 6.423, an NH₃ concentration of 500 μg/dL, and the presence of Parvimonas micra and Prevotella buccae.