Pelvic actinomycosis is a rare disease. Clinical presentation causes diagnostic difficulty, because they are similar to those of advanced pelvic cancer. Long-term use of an intrauterine device can promote overgrowth of actinomyces in the vagina. This can in turn lead to tubo-ovarian abscesses with severe complications. A case is reported of a woman with five-year-use of an intrauterine device. She suffered from pelvic actinomycosis with imaging manifestations mimicking those of pelvic malignancy.