Patients with antisynthetase-positive interstitial lung disease (ILD) alone sometimes develop myositis during follow-up, but myasthenia gravis (MG) overlapping on antisynthetase syndrome is unusual. A 56-year-old woman with ILD and anti-EJ antibody treated for 8 years developed MG. Physicians should consider myositis and MG when patients develop muscle symptoms during follow-up.