A 50-year-old woman had a percutaneous endoscopic gastrostomy (PEG) tube placed after surgery for pharyngeal cancer. After 21 months, the PEG tube was removed due to improvement of per-oral ingestion. She had taken prednisolone for 31 years for systemic lupus erythematosus. The post-PEG fistula did not close spontaneously. The cause of the fistula was slow wound healing and gastrostomy site inflammation due to long-term steroid therapy. We were able to close the fistula with an over-the-scope clipping (OTSC) system. This case suggests that OTSC is useful for closing persistent post-PEG fistulas in patients receiving long-term prednisolone therapy.