Effect of ethanol on the absorption rate, blood level and bioavailability of sulfamethazine (SM) in rats was determined. Absorption rate of SM was determined both by the in vitro and in situ experiment. In vitro, absorption rate of SM in rat small intestine was increased by 0.3, 1.0 and 3.0% ethanol. In situ, absorption rate of SM was increased by 0.3 and 1.0% ethanol but not by 3.0% ethanol. After oral administration, blood level of SM was elevated and relative bioavailability was significantly increased to 114.8% at the dose of 0.6g/kg ethanol but not significantly at the dose of 3.0g/kg ethanol. The time for attainment of peak blood level was changed from 2.5 to 1.5hr. Ethanol enhanced absorption rate constant of SM significantly and reduced elimination rate constant of SM administered orally at the dose of 0.6g/kg ethanol.