Background Studies that examine the growth effects of massage at ages beyond infancy are rare. A recently developed massage chair (BEG-100) targets teenagers who want to increase their growth. The chair can stretch areas around the knee after fixating the knee and ankle areas. Methods This is a clinical study that included 38 children aged 11 years whose heights ranged from 145.0 to 155.0 cm. We aim to observe the potential of a 24-week massage for growth promotion. We will also evaluate the changes in height percentile, height, height standard deviation score, bone age, height standard deviation score for bone age, growth rate, predicted height estimated from bone age, seated height-to-standing height ratio, weight, and body mass index. To confirm safety, the associated adverse events will be investigated. Objective The aim of this study was to investigate the growth-promoting effect of BEG-100 in children with average height. Trial registration KCT0004673 (Clinical Research Information Service).