Various COVID-19 vaccines are associated with numerous adverse side effects. Associations between vaccinations and neurological disorders, such as transverse myelitis, stroke, Bell's palsy, acute disseminated encephalomyelitis, and Guillain-Barré syndrome, have been reported. A 27-year-old Japanese woman presented with paresthesia four days after receiving a second dose of the COVID-19 vaccine. One month after vaccination, she started to feel left lower limb weakness, and her symptoms almost improved after two steroid pulse therapies. Spinal cord tumor biopsy could potentially help make a definitive diagnosis in clinical situations. However, it is very important to review the patient's medical history, including vaccinations received, before performing a direct spinal cord biopsy, which is invasive and does not guarantee a definitive diagnosis.