Peritoneal metastasis of prostate cancer is extremely rare, with only a few cases reported. A 78-yearold male patient was introduced to our hospital presenting with a prostate-specific antigen (PSA) level of 94.0 ng/ml at examination. He was diagnosed with poorly differentiated adenocarcinoma of the prostate, with a Gleasonscore of 9 (5＋4) at cT3bN0M0. Intensity-modulated radiation therapy was performed after 6 months of combined-androgen blockade (CAB) therapy. Twenty-one months later, several lymph node metastases were observed. With the resumptionof CAB therapy, PSA levels dropped and the multiple lymph node metastasis disappeared ; however, peritoneal metastasis was observed after 43 months. We performed a laparoscopic biopsy and our diagnosis after pathological evaluation was metastasis of the prostate cancer. He was treated with Enzalutamide.