A 60-year-old man suffered from inoperable recurrent undifferentiated thyroid cancer and was scheduled to undergo chemotherapy. He had no known allergy to medications. In the first regimen, he was given IV granisetron and betamethasone before IV 120 mg paclitaxel was administered. Five minutes after the paclitaxel infusion, he developed anaphylactic shock of hypotension, dyspnea, and flushing. He was treated by steroid and recovered. In the second regimen one week later, he was scheduled to be treated by other antineoplastic medication instead of paclitaxel for fear of anaphylaxis. Prechemotherapy the same as the first regimen, granisetron and betamethasone, were given,but he developed the same anaphylaxis before the antineoplastic medication was given. He was thus thought to develop anaphylaxis due to the granisetron itself. Anaphylaxis caused by granisetron has not yet been reported, and this experience prompted us to report this case.