Abstract: Subacute thyroiditis (SAT) is the most common self-limiting thyroid disease causing pain. The etiology of the disease remains unknown, but it is usually related to viral infection or allergic reaction after viral infection. SAT after vaccination is extremely rare. The patient had a fever of no clearly defined cause about 8 hours after receiving the first dose of a 0.5 mL 9-valent human papillomavirus vaccine (Gardasil 9). The highest temperature was 37.8 ℃, accompanied by a pain in the neck, fatigue and the increasing pain when swallowing. After the patient was admitted to the hospital, physical examination revealed Ⅱ° enlargement of the thyroid gland, which was hard and tender, and no vascular murmur was heard. There was no redness, swelling or ulceration at the vaccination site, and no obvious abnormalities were observed in other physical examinations. Laboratory findings were as follows: C-reactive protein, 25.20 mg/L; erythrocyte sedimentation rate, 55 mm/1 h; leukocyte, 4.94×10⁹ L⁻¹; thyrotropin, 0.137 mU/L; free thyroxine, 22.32 pmol/L; antithyroglobulin antibody, 69.18 IU/mL; anti-thyroid peroxidase antibody, 21.66 IU/mL. Thyroid ultrasonography showed diffuse enlargement of bilateral thyroid with uneven internal echo. The patient was diagnosed with SAT. After 5 days of treatment with ibuprofen, the patient no longer had low fever and the neck pain was relieved. The patient was followed up till now, and had completed the vaccination of the three-dose 9-valent human papillomavirus vaccine. The function of thyroid was found to be normal in follow-up visits, and SAT did not recur.