Abstract: The reaction system includes 0.1 M GIy-NaoH buffer and the supernatant ofthe homogenate of the grass carp and common carp liver representing the enzymesolution. After addition of CCU,the reaction mixture was incubated at 25℃for 5h. The metabolite was extracted with ethy1 acetate,separated by TLC and identifiedbv HPLC,It was demonstrated that CPU was produced in the mixture,That theproduct was CPU was further verified by spectroscopy,using a specia1 UV detectorwhich could give absolute spectral evidence for the identification of CCU metabolite,and comparing the UV scanning chromatograph for CPU standard with that of themetabolite spot at the certain range of wavelengths. When specific inhibitor of es- terase was applied to the reaction mixture the activity of enzyme was decreased by 89～99 percent.It shows the key role of esterase in the production of CPU.