A case report presents the experience of diagnosis and management of Unicameral Bone Cyst(UBC) of midshaft Humerus. The lesion had a pathognomonic radiologic appearance of Unicameral Bone Cyst and diagnosis was histologically confirmed. We treated operatively by open curettage with auto graft bone augmentation with external fixator and significant improvements was noted in postoperative period. On basis of analysis of treatment results open curettage with auto graft bone augmentation with external fixator. if required, effective procedure Obtaining good functional results and shorter period of treatment.