Yam (Dioscorea opposita) is commonly consumed in East Asia, but allergic reaction to this plant food is rare. To date, there is no report of anaphylactic reaction after ingestion of cooked yam. We described 3 cases with anaphylaxis after eating boiled yam and 1 present with oral allergy syndrome as well. Basophil activation test in patients showed positive reactivity to boiled yam extract. In immunoblotting, a 30-kDa protein was recognized by all patients' sera and a 17-kDa band was detected by 1 patient. N-terminal amino acid revealed the 30-kDa IgE reacted band was DB3S, dioscorin in Dioscorea tuber. It promoted us that DB3S was a thermal stable oral allergen to trigger anaphylactic reaction and oral allergy syndrome in cooked yam (D. opposita) allergy. Patients with this plant food allergy should avoid both raw and well-cooked yam.