Abstract: Weigh fish oil 2 g and add 13 C 12- p,p′-DDT sith almost the same amount as the p,p′-DDT in the weighed fish oil.Mix and add octane till the total volume is 10 mL.Applied the technique of GPC for removing 99% of lipids in fish oil.The GPC system is consisted of a glass preparation column(350 mm×20 mm)with filled material(Bio-beads S-X3,200-400 mesh),a HPLC pump and an UV detector.CH 2Cl 2:hexane=1∶1 as eluent and flow rate is 4 mL/min.Per-injection of the sample into GPC system is 1ml.Detection wavelength is 210 nm.The collected solution from Gpc is blown to dry by N 2.2 mL hexane washes the residue and 0.5 mL of concentrated sulfuric acid destroys the remained lipids.GC-MS-SIM measured the ratio of p,p′-DDT(m/z 234.99)and 13 C 12 -p,p′-DDT(m/z 246.99). A HP SE-30MS capillary column is used.Bracketing is used as quantitative method.Uncertainties of measurement results are not more than 0.6%.Our results are the best ones with the smallest uncertainties in the nine mational laboratories.