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PURPOSE To confirm whether encephalitis due to unknown causes but with normal brain magnetic resonance imaging (MRI) may be associated with the myelin oligodendrocyte glycoprotein (MOG) antibody. METHODS We retrospectively analyzed and summarized the characteristics of three patients initially suspected of having intracranial infections with normal brain MRI, and ultimately tested positive for anti-MOG antibody. RESULTS The three patients mainly presented with long-term fever accompanied by headaches and drowsiness. Auxiliary examinations showed obvious leukocytosis in peripheral blood and leukocytosis and increased protein expression in cerebrospinal fluid (CSF); furthermore, brain MRI was normal. These findings suggested intracranial infection, especially bacterial meningitis. No patient showed a response to prolonged anti-bacterial therapy; however, they recovered with glucocorticoid therapy, which was prescribed after anti-MOG antibodies were detected in the serum and CSF samples. CONCLUSION Anti-MOG antibody detection should be performed early for patients with suspected encephalitis due to unknown causes with normal brain MRI, to identify whether they have MOG antibody-associated diseases (MOGAD).