ABSTRACTLumefantrine has been reported to be mainly bio‐transformed by cytochrome P450 isozyme 3A4 to desbutyl‐lumefantrine (DLF) in human liver microsomes. Since CYP3A is expressed in a sex specific manner in rats, it could be expected that the pharmacokinetics of lumefantrine would be changed in male rats compared with those in female rats. The pharmacokinetics of lumefantrine and its active metabolite DLF were evaluated after intravenous (0.5 mg/kg) and oral (20 mg/kg) administration of lumefantrine to male and female Sprague–Dawley rats. The quantitative bioanalysis was carried out by the liquid chromatography tandem mass spectrometry method. After intravenous and oral administration of lumefantrine the area under the curve (AUC) of lumefantrine was significantly higher in female rats than that in male rats, whereas the AUC of DLF was significantly lower in female rats in comparison with male rats. This lower AUC of DLF in female rats could have been due to reduced metabolism of lumefantrine in female rats. The bioavailability (%F) of lumefantrine was 1.66 times higher in male rats than that in female rats. Copyright © 2012 John Wiley & Sons, Ltd.