Dose-dependent pharmacokinetics of acetaminophen was studied in the rat. Acetaminophen was injected intravenously at doses of 10, 30, 50, 100 and 200mg/kg to the adult male rats. The well-known dose-dependent pharmacokinetic behavior was found even at 30mg/kg dose. It implies that metabolism of acetaminophen in the liver, probably sulfation, is saturated at very low concentration of acetaminophen. Dosage regimen establishment based on this characteristics would be necessary even at usual does level (300-600mg/day/body).