Polymyositis is characterized by non-specific inflammatory disease associated with an autoimmune disorder involving muscles of the limbs and neck. We report a case of an 80-year-old man who was referred to our clinic with a chief complaint of dysphagia and muscle weakness in all four limbs. The patient was diagnosed with polymyositis based on pathological findings, muscle weakness, electromyogram findings, and an elevated creatine phosphokinase level. The patient was also positive for HLA-DR3. Intravenous predonine administration was initiated, but dysphagia was not improved. We considered a cricopharyngeal myotomy, but this could not be performed because of heart failure. Endoscopic balloon dilation was performed and dysphagia improved on the same day. Therefore, we suggest that this method is a safe and effective approach for polymyositis with dysphagia.