Jing song ling (2,4-xylidinothiazoline, XT) is a new anesthetic agent for veterinary uses in China. From urine of rats given the drug three metabolites (MA1, MA2 and MB3) were isolated with structure shown in page 98 in addition to the parent compound (MB1). Preliminary observations showed that the toxicity and pharmacological activity of MB3, MA2 and MA1 decreased significantly compared with the parent drug XT. Species difference of biotransformation of XT between rat and mouse was also observed.