Tumors that cause osteomalacia are generally benign fibroblast growth factor-23 producing mesenchymal tumors which can be detected by octreoscan. A 45-year-old man underwent (99m)Tc-HYNIC-TOC scan to detect a possible culprit causing osteomalacia. The images showed abnormal activity in the left humerus and in the right foot. The lesion of the right foot was confirmed pathologically as phosphaturic mesenchymal tumor. After surgical removal of the tumor in the right foot, the patient's symptoms were promptly improved. However, the improvement was transient due to the unresected tumor in the left humerus.