(S)-2-Ethoxy-3-(4-{3-methyl-5-[4-(3-methyl-isoxazol-5-yl)-phenyl]thiophen-2-ylmethoxy}-phenyl)-propionic acid (PAM-1616) is a novel peroxisome proliferators-activated receptor γ (PPARγ) partial agonist with excellent antihyperglycemic activity. It is a promising new drug candidate for the treatment of type-2 diabetes with reduced possibility of edema in vitro/in vivo. In order to evaluate the pharmacokinetics of PAM-1616, a reliable, selective and sensitive highperformance liquid chromatography/electrospray ionization tandem mass spectrometry was developed for the quantification of PAM-1616 in rat plasma. The analytes were extracted from rat plasma with ethyl acetate, separated on an Atlantis dC(18) column with a mobile phase of 75% acetonitrile in 10 mM ammonium formate (pH 4.5), and detected by tandem mass spectrometry in the selective reaction monitoring mode. The calibration curve was linear (r (2) = 0.999) over the concentration range of 0.05-20.0 μg/mL and the lower limit of quantification was 0.05 μg/mL. The coefficient of variation and relative error at four QC levels were 1.8% to 14.3% and -10.0% to 6.5%, respectively. The present method was successfully applied to the pharmacokinetic study of PAM-1616 after intravenous administration of PAM-1616 potassium at a dose of 1 mg/kg in rats.