The usefulness of nasal irrigation for chronic rhinosinusitis is recognized, and it is widely used as a topical treatment after endoscopic sinus surgery (ESS). Generally, there are few complications due to nasal irrigation, and it is recognized as a highly safe treatment. There are no reports of nasal septal perforation due to nasal irrigation. The objective of this study was to describe three cases of nasal septal perforation occurring during self-nasal irrigation after ESS. Case patient 1 was a 38-year-old woman who was admitted to our hospital with a complaint of nasal obstruction. Based on a diagnosis of chronic rhinosinusitis and allergic rhinitis, we performed bilateral ESS and bilateral inferior turbinectomy. At discharge, we instructed the patient in how to perform self-nasal irrigation twice a day at home. At the time of the third visit after discharge, a black crust had adhered to the bilateral anterior nasal septum. Crust formation continued at the same site, and nasal septal perforation was seen two and a half months after the operation. The other two cases showed similar courses. Postoperative nasal irrigation can cause nasal septal perforation. We need to educate patients on proper nasal irrigation and regularly check the nasal septum.