Cholesterol granuloma (CG) is a histological lesion caused by an inflammatory reaction of the cholesterol crystal rather than an independent disease. We report the case of an 87-year-old woman who came to our hospital for slight abdominal pain lasting a week and who had a history of a pelvic mass found forty years ago. Ultrasound examination revealed abnormal omentum, which was suspected to be a source of metastasis from the pelvic mass. However, ultrasound-guided biopsy confirmed the abnormal omentum was CG. By describing this case, we aim to share the value of ultrasound-guided omentum biopsy in clinical diagnosis and treatment.