A 50-year-old man underwent thorough examination for a chief complaint of melena. Gastric cancer and right kidney cancer were diagnosed. The gastric cancer was in the antrum, and poorly differentiated adenocarcinoma was diagnosed by biopsy. The right kidney cancer was diagnosed as clear cell carcinoma by computed tomography-guided biopsy. We performed right nephrectomy and distal gastrectomy. The final diagnosis of the gastric cancer was por2, pT3( ss), pN3b( 46/ 61), M0, pStage IIIB, R0, and that of the kidney cancer was clear cell carcinoma, pT3a, pN0, pM0. The patient reported lower back pain approximately 2 months after surgery. Several examinations revealed that the patient had multiple bone metastases, disseminated carcinomatosis of the bone marrow, and disseminated intravascular coagulation (DIC).We treated the bone metastasis with denosumab and palliative radiation therapy and the gastric cancer with weekly paclitaxel (PTX). The DIC subsided during the first course but recurred during the discontinuation period. We attempted additional trastuzumab treatment but did not achieve a curative effect, and the patient died. It is necessary to provide appropriate medical care while taking into consideration the possibility of disseminated carcinomatosis of the bone marrow in cases with a high likelihood of lymph node metastasis.