We describe a case of asymptomatic struma ovarii in a 61-year-old woman who presented with elevated thyroglobulin level during checkup. Tc-99m pertechnetate whole-body scintigraphy showed a normal thyroid uptake, and an increased uptake localized on the upper left side of the urinary bladder corresponding to the ovary. Pelvic SPECT/CT confirmed increased uptake localized in left adnexal area. Histopatologic verification confirmed the diagnosis of struma ovarii. We report an unusual case of incidental diagnosis of struma ovarii with Tc-99m pelvic SPECT/CT imaging.