This study was planned as a randomized, controlled, single-blind study. The aim of this study was to investigate the effects of graded motor imagery (GMI) training, performed in addition to conventional treatment of patients with obstetric brachial plexus injury, on upper extremity motor function, proprioception, functional mobility and quality of life. In parallel to the initial assessment, a conventional physiotherapy program was created that is individualized according to the functional status and severity of the effects in the children. In the GMI program, in addition to this program, the components of GMI training are applied to sequentially activate the cortical motor networks and develop cortical organization. All assessments of the participants before and at the end of the treatment are carried out by a blind physiotherapist.