A 65-year-old man with dysuria was referred to our department with a prostate-specific antigen concentration of 145.6 ng/ml. Unenhanced T2-weighted magnetic resonance imaging showed high signal intensity mainly in the right lobe of the prostate and a mass lesion with a mucus component. Contrastenhanced magnetic resonance imaging showed a progressively increasing contrast effect in the same region. Prostatic biopsy was performed, and histopathology revealed a Gleason score of 4＋3＝7, and a diagnosis of mucinous carcinoma of the prostate, stage cT3bN0M0. The patient underwent robot-assisted laparoscopic total prostatectomy and enlarged lymph node dissection. Pathological analysis confirmed mucinous adenocarcinoma of the prostate, with a Gleason score of 4＋3＝7, EPE1, RM0, ly1, v0, pn1, sv0, n1 (1/22). The final pathological diagnosis was prostate mucinous carcinoma, pT3aN1M0, and strict post-operative two-year follow-up resulted in no biochemical recurrence (prostate-specific antigen concentration was 0.001 ng/ml). The results suggest that surgical treatment may provide a good prognosis in high-risk prostatic mucous carcinoma.