Abstract: Objective To analyze the ultrasonographic features of patients with Riedel's thyroiditis and improve the accuracy in ultrasonic diagnosis. Methods Thirteen patients who were diagnosed as Riedel's thyroiditis in our hospital from June 2004 to June 2014 served as observation group, and another 13 cases with thyroid cancer that might be easily confused with this disease in this period served as control group. All patients underwent ultrasound examination and their ultrasonic features were compared. Results The thyroid nodules in observation group showed heterogeneous echo, less clear boundary, no obvious echo envelope, and the anteroposterior diameter/transverse diameter was less than 1 without lymph node metastasis. The thyroid cancer in patients of control group showed uneven echo, unclear boundary or partly unclear boundary, the anteroposterior diameter/transverse diameter was less than 1 with frequent lymph node metastasis. The aspect ratio of observation group and control group was greater than 1, micro calcification and lymph node metastasis showed significant difference (P< 0.05). Conclusion The main two-dimensional ultrasound image shows heterogeneous echo, no obvious echo envelope, unclear boundary, and the aspect ratio is less than 1 without any abnormal neck lymph nodes.