The diagnosis of mucinous adenocarcinoma of the prostate (MAP) requires that at least 25% of the tumor consists of pools of extracellular mucin. According to the above criteria, MAP is rare and about 70 cases have been reported in literature. Here we report a case of MAP arising in a 70-year-old man. In the present case, the proportion of the mucinous component was up to 95% of the total tumor volume, and Gleason's score is 8 (4+4). The tumor cells were prostatic specific antigen (PSA)-immunoreactive in mucinous and nonmucinous components. Despite the mucin pools, the tumor cells themselves failed to stain with any of the mucin stains.