Background and purpose: DKA is a serious complication of relative insulin deficiency that can occur in type 1 and type 2 diabetes mellitus. One of the most common complications in autoimmune disorders is pericarditis but it is very rare in DKA. Case Report: The patient is an 8-year-old girl who was admitted with weakness, lethargy, dizziness and fever. Blood sugar of 490 mg/dl and acidosis with ketoneuria demonstrated DKA. During hospitalization, due to abdominal and chest pain echocardiography were done, and moderate to severe pericarditis and pericardial effusion were reported. Conclusion: DKA is a serious complication of relative insulin deficiency that occurs during diabetes and epidemiological data showing a steady increase in its incidence in children. Immunodeficiency effect of diabetes and hyperglycemia can cause complications in DKA patients. Understanding mechanisms of complications such as pericarditis is important in decreasing morbidity and mortality and also appropriate treatments.