Recently, laparoscopic techniques are being increasingly used for retroperitoneal surgery. These procedures are considered relatively safe and non-invasive, however, there exists a small but important risk of developing complications related to insufflation with carbon dioxide (CO2). A 51-year-old female patient was admitted for retroperitoneal laparoscopic nephrectomy under general anesthesia. About 60 minutes after carbon dioxide pneumoperitoneum, the patient's oxygen saturation decreased. A chest x-ray was taken in the operating room, which showed pneumothorax in the right lung. We concluded that anesthesiologists should be aware of the occurrence of pneumothorax during the retroperitoneal laparoscopic procedure careful monitoring and appropriate management are needed.