Introduction: Gossypiboma is a rare tumor caused by gauze fibers retained during surgery. This medico-legal problem is associated with an increase in patients’ morbidity and mortality. The aim of this study is to report two cases of gossypiboma mimicking the imaging of a malignant tumor. Case Presentation: We report two patients (the first patient was 50 years old, with a history of an appendectomy three years ago in another city; the second patient was 52 years old, with a history of a cesarean section 25 years ago in another hospital) who were admitted to the oncology department of GhaemHospital, Mashhad University of MedicalSciences in 2014. The initial manifestations were signs and symptoms of malignant ovarian tumors, and abdominal ultrasounds and CT scans also indicated malignant tumors.Both patients had a history of a previous laparotomy.Surgical evaluation confirmed gossypiboma as a definite diagnosis. Conclusions: In patients with abdominal or pelvic masses and a history of previous abdominal surgery, the possibility of gossypiboma should be kept in mind.