Acetamiprid belongs to a new class of insecticides called neonicotinoids, which have different effects from other insecticides. Neonicotinoids act as selective agonists at the nicotinic acetylcholine receptors, therefore their toxicity is higher to insect pests than to humans. Cases of acetamiprid poisoning are still rare, because neonicotinoids have been released in the market only within the last decade. We experienced a case of acute acetamiprid poisoning and measured the blood concentration of acetamiprid. A 79-year-old man had ingested acetamiprid and got medical attention two hours after ingestion. On arrival, he had consciousness disturbance (GCS-8), hypotension, nausea, vomiting and hyperglycemia, but had no constricted pupils nor mucous supersecretion which are characteristic in organophosphate poisoning. Gastric lavage was performed and activated charcoal and laxative were administered. Paroxysmal atrial fibrillation persisted until 11 hours after ingestion. The next day, his symptoms with regards to the effects of acetamiprid improved and he was discharged from the hospital without complication. Blood concentration of acetamiprid on arrival, approximately 2 hours after the ingestion, was 21.1 microg/ml.