Pelvic actinomycosis is an uncommon chronic granulomatous disease that is caused by actinomycosis Israeli. The most risk factor is long-term use of IUD. In this article we dealt with a 42 year old woman, who referred to the hospital with a history of intrauterine device (IUD) use for 15 years, having nonspecific lower abdominal pain, low grade fever, and occasional chills for 2 months, On pelvic examination a mass was found. Clinical findings, sonogrphy, CT scan and barium enema strongly suggested a pelvic malignancy. After laparatomy and histological examination, pelvic actinomycosis was diagnosed. The patient was given penicillin, for a long term. In patients with abdominopelvic pain, pelvic mass and adhesion, specially long-term IUD using, actinomycosis is probable; and by using secretions culture, pap smear, sonography and CT scan diagnosis is promoted before surgery to avoid an unnecessary action.