The rete ovarii is a rare site for tumor development. We present a case of cystadenoma originating from the rete ovarii of a 58-year-old woman. It was a unilocular cyst of 7.0 cm in size, lined by flat, cuboidal, or columnar epithelial cells supported by fibromuscular tissue. Papillary growth and crevice formation of the inner surface were characteristic. The presence of a normal rete ovarii was helpful in correct diagnosis.