Abstract: Residual amounts of chlorthalomil and triadimefon in onion sample were determined by GC with nitrogen-phosphorus detector (NPD).The insecticides in sample were extracted with H3PO4 acidified acetonitrile and the extract obtained was purified and concentrated on Florisil column with petroleum ether-acetone (1+1) as eluant.The eluate from column was evaporaed to dryness by N2-blowing and the residue taken up with 5.0 mL of n-hexane,which was used for GC analysis.External standard calibration was adopted in the determination.Linear relationship between values of peak area and mass concentration of chlorthalomil and triadimefon were obtained in ranges of 0.05-5.0 and 0.1-5.0 mg·L-1 respectively,with detection limits of 0.02 mg·kg-1.Test for recovery was made by standard addition method,giving results in the ranges of 84.5%-90.2% (chlorthalomil) and 92.1%-101.0% (triadimefon).Values of RSD′s (n=6) found were less than 5.5%.