Zygomycosis is usually an invasive mycotic disease caused by fungi in the class Zygomycetes. It often occurs in immunocompromised patients, but sporadic cases without apparent immune impairment have been described. This report presents the first case of pleural zygomycosis caused by Rhizomucor pusillus, an uncommon pathogen of human infection. A 19-year-old man was found to have pleuritis several days after a drainage catheter was implanted to cure a pneumothorax caused by a ruptured bulla. Local pneumonectomy to resect the ruptured bulla and vacuuming of the pleural fluid was performed. Rhizomucor pusillus was cultured from the pleural fluid and irregular broad sparsely septate hyphae, consistent with zygomycetes, were histologically detected in the thickened pleura of the resected bulla. The catheter was suspected of having been contaminated with the fungus, but no evidence could be obtained. His fungal pleuritis subsided without any antifungal medical therapy and his immunocompetence seemed to contribute to limiting the infection.