The occurrence of malignant mural nodule in benign cystic common epithelial tumor of the ovary have been reported in only three cases; the case one was mucinous cystadenoma with a mural nodule of fibrosarcoma and the others were of carcinomas. Our case was another rare case of ovarian mucinous cystadenoma with mural nodule of anaplastic carcinoma in a 42-year-old woman. The cystadenoma had an unilocular cystic cavity and a mural nodule with thick multinodular solid wall. The internal cystic wall was lined with mucinous cystadenoma without any malignant features. The mural nodule showed anaplastic carcinomatous differentiation and its nature was confirmed by immunohistochemistry and electron microscopy. This tumor had metastasized to the right salpinx, uterus, cul-de-sac, periureter and mesentery.