Immune-related adverse events (irAEs) caused by immune checkpoint inhibitors (ICIs) have been widely documented. Diabetic ketoacidosis (DKA), a severe irAEs, has not been previously reported in patients with nasopharyngeal carcinoma (NPC). This case report describes the development of DKA during maintenance immunotherapy with tislelizumab in a patient with recurrent NPC. A 41-year-old female patient with recurrent NPC (rT3N0M0, 8th edition of AJCC staging) experienced DKA during her 13th session of maintenance treatment with the ICI tislelizumab. After urgent consultation with an endocrinologist, immune-related DKA was diagnosed, and immune checkpoint inhibitor-related diabetes was confirmed. Prompt treatment with hypoglycemic agents, fluid infusion, and correction of water-electrolyte and acid-base balance was administered. The patient's blood glucose was stabilized within 6 days, and she was discharged without complications. This is the first reported case of DKA in a patient with NPC receiving tislelizumab maintenance immunotherapy. Clinicians should enhance their understanding and monitoring of adverse events in patients treated with ICIs, focusing on early diagnosis and appropriate intervention.