Celery (Apium graveolens) is a popular medicinal herb that used conventionally for the treatment of different diseases. This report aimed to demonstrate celery would induce hyperthyroidism after oral celery extract consumption for weight loss. A 36-year-old female patient came to our clinic with blurred vision, palpitation, and nausea. Dietary history showed that she used 8 g/day of celery extract in powder form for weight reduction. Weight loss during 78 days of celery extract consumption was 26 kg. Thyroid function test showed that serum level of thyroid-stimulating hormone (TSH) and T4 were 0.001 mIU/L and 23 ng/dl, respectively). Grave's and thyrotoxicosis ruled out by other laboratory evaluations. Methimazole 10 mg/day was prescribed. Serum level of TSH was evaluated. The celery extraction intake was discontinued when started treatment with methimazole. Not found any thyroid stimulator (thyroxin and other) in celery extraction. We concluded that observed hyperthyroidism and allergic reaction may be induced by celery extract consumption. Therefore, it is possible that hyperthyroidism may be a side effect of frequent celery extract consumption.