Purpose : To demonstrate the radiologic characteristics of the pelvic actinomycosis. Materials and Methods : We retrospectively reviewed the radiologic findings of seven patients with pathologically proven pelvic actinomycosis and analyzed the anatomical location, characteristics of the lesion and alteration of surrounding structures. Results : The location of the lesions were the ovary and adnexa(n = 4), rectum(n = 1), cecum and terminal ileum(n = 1), and bladder(n = 1). Three of the seven patients had a past history of intrauterine devices. Post-contrast enhanced CT showed an ill-defined mass with inhomogeneous enhancement and a tendency to invade the surrounding normal tissue plane. Conclusion : Pelvic actinomycosis should be included in differential diagnosis when an unusually aggressive infiltrative mass is located in the pelvic cavity, especially in a patient with long-term use of intrauterine contraceptive devices.