We here report 2 cases of castration-resistant prostate cancer (CRPC) observed two times on 11C-choline positron emission tomography computed tomography (PET/CT), which was useful to discriminate viable progressive osteoblastic bone metastasis from benign osteoblastic change induced by the treatment effect and to determine the viability of bone metastases, regardless of whether sclerosis was present or not. Because one case demonstrated disappearance of abnormal 11C-choline uptake of osteoblastic metastatic lesions after abiraterone therapy and no new lesions at other sites, suggesting nonviable bone metastases, we can assume a complete metabolic response. Because the other case demonstrated a decrease in the existing, abnormal 11C-choline uptake of osteoblastic metastatic lesions, but multiple new appearances of osteoblastic and nonosteoblastic lesions with abnormal 11C-choline uptake after radium-223 therapy suggesting multiple viable bone metastases, we can assume progressive metabolic disease. 11C-choline PET/CT could help in assessing the treatment response of bone metastases in patients with metastatic CRPC.