Abstract: A GC-MS method for the investigation on the metabolism of n-butyl phthalide(NBP)is described.After oral administration of NBP to rats,urine was collected,hydrolyzed with β-glucuronidase, extracted and concentrated for TMS derivatization,and then analyzed by GC- MS.HBP and its four oxidative metabolites were determined in 0～24h,24～48 h rat urine.The massspectra of the metabolites and their derivatives were presented and the in vivo metabolic pathway wasdiscussed.