Abstract: Aflatoxin B1 (AFX B1) in fructoside of fructus momordicae was determined by HPLC with pos-column derivatization.MYCOTOXTM C18 was used as reversed-phase chromatographic column (4.6 mm×250 mm),and a mixture containing methanol,acetonitrile and water in the ratio of 22+22+56 was used as mobile phase.A water solution of iodine (100 mg·L-1) was used the derivatizing reagent.Measurement was made by fluorescence detector with λex 365 nm and λem 430 nm.Linear relationship between peak area and mass concentration (mg·L-1) was shown by the linear regression equation,y=14.222 x+0.625 3 (r=0.998).Tests for recovery and precision were performed at 3 different concentration levels (5.1,40.8 and 102 μg·kg-1 of AFX B1),and values of recovery and RSD′s (n=10) obtained were in the ranges of 81.4%-94.2% and 2.1%-4.5% respectively.