A 57-year-old woman presented with abnormal sensations and muscle weakness in the left upper and lower limbs and difficulty in walking four days after coronavirus disease 2019 (COVID-19) vaccination. The patient had deep sensation deficits and increased tendon reflexes in the left upper and lower limbs. Her head and cervical spinal cord magnetic resonance imaging showed a ring-shaped contrast-enhancing lesion. Cerebrospinal fluid examination showed a mildly elevated cell count, myelin basic protein, and IgG index, and positive oligoclonal bands. The patient was diagnosed as inflammatory demyelinating diseases of the central nervous system (IDDCNS) due to vaccination and was treated with pulse steroids. Her symptoms improved to a greater degree compared to previously reported cases of IDDCNS after COVID-19 vaccination. The disease course of this case was monophasic, but was more similar to multiple sclerosis than to acute disseminated encephalomyelitis (ADEM) according to their diagnostic criteria. Careful long-term observation is necessary because vaccination, as in this case, may lead to relapses in multiple sclerosis (MS) patients who have not received disease-modifying drugs.