The in vivo metabolism of 2,5-dimethoxy-4-ethylthiophenethylamine (2C-T-2) and 2,5-dimethoxy-4-isopropylthiophenethylamine (2C-T-4), new psychoactive drugs, were studied using rats. 2C-T-2 hydrochloride and 2C-T-4 hydrochloride were administered separately to male Sprague-Dawley rats via the oral route (10 mg/kg), and the urinary extracts were analyzed by liquid chromatography/mass spectrometry. Fourteen and ten metabolites for 2C-T-2 and 2C-T-4 were detected in the urinary extracts, respectively. Our results suggested that sulfoxidation, sulfone formation, S -dealkylation followed by S -methylation, N -acetylation and deamination followed by oxidation were the major metabolic pathways of 2C-T-2 and 2C-T-4 in rat.