Introduction: The acute mesenteric ischemia (AMI) is a fatal vascular emergency disease that had a high mortality and morbidity. It is generally occur in older patients, and rare condition in children. Furthermore, it was unusual that a child diagnosed with new-onset type I diabetes mellitus (T1DM) who developed acute mesenteric ischemia secondary to severe dehydration and hyperosmolarity. Altough hypernatremia could present in patient who was severely dehydrated and had diabetic ketoacidosis, but severe hypernatremia was extremely rare Case: A 13-year-old previously healthy girl was brought to emergency center of our hospital for vomiting and progressive lethargy lasting 3 days. She had a 1-month history of polyuria and polydipsia and a reported weight loss of 13 kg over a period of 1 month. Upon admission to the emergency department, the patient was confused and appeared acutely sick and markedly dehydrated. Laboratory test results on admission for the patient was as follows: serum glucose, 1330 mg/dL; serum sodium, 162 mEq/L; serum osmolarity, 441 mOsm/L; pH, 7.15, respectively. Plain x-ray of her abdomen was revealed only mild paralytic ileus. After initial hydration, her consciousness was slightly recovered with orientation of her name and age. And, her followed up laboratory test results were; serum glucose, 605 mg/dL; serum sodium, 160 mEq/L; and serum osmolarity, 421 mOsm/L. However, the patient’s consciousness level was acutely worsened and abdomen was distended 8 hours after admission. Emergent abdomen computer tomography scan was performed, and the images consistent with pneumatosis intestinalis and mesenteric ischemia. Massive fluid resuscitation was done, though, the patient was suddenly died about 4 hours after diagnosis. Conclusion: We report a case that diagnosed with new-onset type I diabetes mellitus (T1DM) who developed acute mesenteric ischemia secondary to severe diabetic ketoacidosis and hyperosmolar hypernatremia.