The osteoblastic activity of carcinoma is restricted in osteoblastic metastasis, common in the patients with prostate cancer, whereas its mechanism and the factors involved are unknown. Here, we present a case of central adenocarcinoma showing the osteoblastic activity in the mandible of the 80-year-old Korean male who had suffered from the paresthesia of lower lip during four mouths. Clinically the overlying oral epithelium was intact, but the radiologic images revealed the ill-defined radiolucent intraosseous lesions in left ascending ramus. Microscopically, the mandibular lesion was composed with carcinoma of ductal or glandular differentiation but lack typical features of any epithelial salivary gland malignancies. Intriguingly abundant new bone formation was found in the stroma, but the tumor cells expressed no reactivity for prostate-specific antigen(PSA). The patient had low ionized calcium level, normal serum alkaline phosphatase and PSA level. Positron emission tomography-computed tomopraphy scan revealed the benign prostatic hyperplasia, but failed to trace the primary site of tumor other than mandible. Therefore, pathologically diagnosis for the lesion was informed as adenocarcinoma, not otherwise specified(NOS). Because occult primary tumor associated with osteoblastic metastasis cannot be completely ruled out, periodic and careful check-ups for the patient should be performed.