Abstract: Similar to eserine, Cui Xing NingCXN),5-(1,3,3-trimethylindoline) N, N-dimethyl carbamate is a choline esterase (ChE) inhibitor. The biotransformation of CXN, whicch had been studied in vivo, and in vitro unsuccessfully, was studied by using isolated perfused rat liver (IPL) method. Six metabolites of CXN from the perfusate were seperated by HPLC, and identified with MS, ¹HNMR or compared with the-authentic compounds. Metabolite Ⅰ Is unchanged CXN, the others, are oxidized metabolites. Most of the metabolites lost their activities of ChE inhibition strikingly except metabolite Ⅲ which retained the 2-position unchanged. The toxicities of some metabolites (Ⅱ, Ⅴ) decreased obviously.