Miller Fisher syndrome (MFS) is characterized by ataxia, areflexia, and ophthalmoparesis. Here we present a case of MFS mimicking Wernicke encephalopathy (WE) during pregnancy. A 31-year-old woman at 8 weeks of gestation presented with diplopia and ataxia after experiencing nausea and vomiting for several weeks. We initiated thiamine based on a suspicion of WE, which produced no clear effects. However, her symptoms began to improve following intravenous immunoglobulin treatment, and other findings finally lead to a diagnosis of MFS. Because ataxia and ophthalmoparesis can be misdiagnosed as WE during pregnancy, clinicians should consider MFS in the differential diagnosis.