A method for determination of nilestriol in the fish by coupling direct insertion probe with mass spectrometer was established. When the fish be dewatered, nilestriol can be drawed with chloroform and the analysis can be made by coupling direct insertion probe with mass spectrometer as the primary temperature at 100℃ and maintains for 30s, then the temperation rised to 300℃ at the rate of 150℃ · min^-1 and kept for 30s. The ratio of signal to noise(S/N) of nilestriol is 14 : 1 as the sample content is lng. The method issimple in operation and sensitive.
