BACKGROUND Bevacizumab is an antiangiogenic agent, and that synergizes with chemotherapeutic drugs. When used in combination therapies, Bevacizumab is associated with adverse events such as hemorrhage, gastrointestinal perforation, delayed wound healing, and pneumothorax. However, the molecular mechanisms underlying these adverse events are not fully understood. CASE SUMMARY A 45-year-old female with multiple lung metastases that were derived from primary breast cancer, was placed on Bevacizumab + paclitaxel therapy, since this combination has a potent antitumor effect. She reported dyspnea before cycle 3, day 1 and we therefore ran a chest X-ray, which detected a right pneumothorax. The coronal plane computed tomography revealed that one solid mass rapidly necrosed and was replaced by a cavity that passed through the bronchus in the right lower lobe. The cavity eventually ruptured the pleura and made the bronchopleural fistula that led to this pneumothorax. Thoracic cavity drainage using an intercostal catheter was performed. On the 7th day of drainage, the patient was discharged from our hospital on recovery. Recurrence of pneumothorax was not reported, and continuation of chemotherapy was made possible by changing the regimen. CONCLUSION Patients with lung metastases surrounding the bronchi and on the pleura should be monitored for pneumothorax by Bevacizumab-containing chemotherapies.