Although endoscopic transmaxillary repair of orbital floor fractures is a minimally invasive treatment, controversy remains regarding the method for supporting the orbital floor after elevation of the orbital contents. To date, a urethral balloon catheter has been widely used. However, it can be difficult to leave the catheter in place for a long time period due to the inconvenience, and prolapse of the orbital contents may recur in the case of its premature removal. This study described the techniques for endoscopic reduction and use of a balloon for orbital floor fractures. From June 2006 through November 2011, 30 of 52 patients (57.7%) with an isolated orbital floor fracture underwent endoscopic transmaxillary repair. A maxillary sinus balloon (#3007, Koken Co., Japan) was inserted into the maxillary sinus to support the orbital floor after endoscopic transmaxillary reduction, and the connecting tube of the balloon was pulled into the nasal cavity through the maxillary ostium. After confirmation of accurate reduction by postoperative CT, the connecting tube was shortened and hidden in the nasal cavity. The balloon was left in place for 4-8 weeks, and then removed via the maxillary ostium on an outpatient basis. Complete resolution of the preoperative diplopia was achieved in 93%, and no late-developing enophthalmos was seen in 97% of the patients. There were no significant complications. This technique is safe and permits prolonged retention of the balloon, without interfering with daily life.