Aneurysmal bone cyst is a rare benign tumor of the bone that can be difficult to distinguish from malignant tumors, especially when it presents in an unusual location. Herein, we report a six-year-old girl with a primary aneurysmal bone cyst in an uncommon location. It originated from the 4th rib and she presented with a huge chest wall mass. Despite the large size of the cyst, the only symptom was persistent cough. She was successfully treated with total excision of tumor without any complication. The patient has been followed up for 56 months without any recurrence.