Pneumothroax may occur during and after general anesthesia unexpectedly, and the diagnosis may be difficult when the manifestations are non-specific. An early diagnosis and treatment is important to prevent tension pneumothorax. Pneumothorax can be occurred from injury to the chest wall, airway, lung, and diaphragm. We report a case of a 50-year-old female patient who underwent segmentectomy of liver under general anesthesia and developed pneumothorax after restoration of spontaneous respiration from unexpected diaphragm injury.