As coronavirus disease 2019 (COVID-19) has spread worldwide, the rate of COVID-19 vaccination uptake is encouraging. Neurological complications associated with COVID-19 vaccines such as stroke, Guillain-Barré syndrome, and Bell’s palsy have been reported.Recently, late-onset myasthenia gravis (MG) following COVID-19 vaccination has been reported. To date, however, there has been no evidence of increased risk of early-onset MG following COVID-19. Here, we report a case of a patient with new-onset MG that arose after receiving a COVID-19 vaccine. A 33-year-old woman suddenly experienced generalized weakness and diplopia on the evening she had received the second dose of the PfizerBioNTech COVID-19 vaccine. The temporal relationship suggests that this new-onset MG is related to the vaccination. It also implies that COVID-19 vaccination could trigger early-onset MG symptoms in patients at risk of MG.