A 68-year-old man was diagnosed with prostate cancer (initial serum prostate specific antigen [PSA] 389 ng/ml, stage cT4N1M1c, Gleason score 5+4), and androgen deprivation therapy was initiated. Despite the low serum PSA level, he developed postrenal acute kidney failure 4 years later, with progression of prostate cancer and liver and lung metastases. Serum levels of neuron-specific enolase and pro-gastrinreleasing peptide (tumor markers) were elevated. He underwent re-biopsy of the prostate, and histopathological examination revealed small cell carcinoma. He was initially treated with carboplatin and etoposide therapy. Liver metastases showed partial remission, and serum tumor marker levels were temporarily reduced. However, disease progression was observed after 4 chemotherapy cycles, and he was then treated with an 8-cycle course of amrubicin. Metastases showed shrinkage, and serum tumor marker levels were reduced after 2 chemotherapy cycles. Tumor enlargement recurred after 8 cycles, and the patient is being treated with palliative therapy. Amrubicin therapy may be effective in the treatment of small cell carcinoma of the prostate.