We report a patient with adult-type Pompe disease treated with enzyme replacement therapy (ERT) for 5.5 years. We evaluated pulmonary function and muscle strength using 6-minute walk test, manual muscle test, and dynamometer-based measurement. The long-term ERT resulted in a substantial improvement in the pulmonary function and a possible stabilization followed by mild deterioration in muscle power measured by dynamometer and 6-minute walk test. Our data may rationalize the long-term use of ERT for adult-type Pompe disease in terms of maintaining pulmonary function.