【Abstract】Objective To discuss the value of SPECT-CT 99mTc-MIBI dual-phase imaging in the precise localization of mediastinal ectopic parathyroid in secondary hyperparathyroidism. Methods A total of 98 patients with secondary hyperthyroidism underwent 99mTc-MIBI dual-phase planar and SPECT imaging. All SPECT imaging combined CT scan. Analysis and localization of fusing images were focused on the abnormal radionuclide foci in mediastinum. Results Six mediastinal ectopic parathyroid glands were found (6/98, 6.1%). In the 4 patients after parathyroidectomy, 3 cases were found to have a solitary ectopic parathyroid in mediastinum, and one case had two ectopic parathyroid glands located in the left lobe of thyroid and mediastinum. In the 2 cases treated with medication, one case was found to have a solitary ectopic parathyroid in mediastinum, and one had two ectopic parathyroid glands located in the right posterior lobe of thyroid and mediastinum. Conclusion 99mTc-MIBI SPECT-CT imaging makes a true fusion of anatomical and functional images. This method provides the most effective approach to detect ectopic parathyroid, and helps surgeons limit operation area, shorten operation time and move the gland easier