Abstract: Objective: To summarize the characteristics of postpartum thyroiditis (PPT) with thyroid peroxidase antibody (TPOAb) negativity combined with postpartum Graves'disease (PPGD) to increase awareness of this disease.Methods: The clinical data of a patient with PPT combined with postpartum Graves'disease (GD) attending the First Affiliated Hospital of Guangxi Medical University in 2021 were collected and relevant literature was reviewed.Results: The patient presented with hypermetabolic symptoms more than 4 months after delivery without characteristic signs of GD.Laboratory tests showed that triiodothyronine (FT₃) and free thyroxine (FT₄)were significantly elevated, thyroid stimulating hormone (TSH) was lowered, accompanied by TRAb positivity and TPOAb negativity, and the hypermetabolic symptoms improved rapidly after ATD treatment, but the thyroid function was decreased abruptly and even the hypothyroidism appeared within 3 months after treatment.Ultrasound examination indicated that PPT was more likely to be combined with GD, and PPT combined with PPGD was confirmed by the thyroid fine-needle aspiration biopsy.Conclusion: Thyrotoxicosis occurring within 1 year postpartum should be considered firstly as PPT and also due to PPGD.When necessary, the thyroid fine-needle aspiration biopsy is feasible to be performed to avoid misdiagnosis and missed diagnosis.