Kienbock's disease, which is an idiopathic osteonecrosis and collapse of the lunate bone, is an uncommon disease in children. This report describes a case of an 11-year-old girl, who presented with avascular necrosis of lunate bone confirmed by radiographic and magnetic resonance imaging evidence. After a short period of casting, the case was fully recovered within one year. The signal change was confirmed by magnetic resonance imaging, and the deformity of lunate that was demonstrated by avascular necrosis. The patient wore a long arm cast for six weeks, and after one year radiographic pattern was normalized.