We report the case of a 15-year-old Japanese girl with myopathy associated with antibodies to a signal recognition particle (anti-SRP myopathy). The patient presented with progressive symmetrical proximal muscle weakness that caused difficulty in walking within 3months, and marked elevation of the serum creatine kinase levels. A skeletal muscle biopsy revealed active necrotic and regenerating processes, with mild inflammatory changes. Based on the above findings, the patient was diagnosed as having anti-SRP myopathy. Only a limited number of pediatric patients with anti-SRP myopathy has been reported previously, with usually a poor prognosis. Early diagnosis is important for obtaining a better prognosis in patients with anti-SRP myopathy.