Objective A method for determination of Δ⁹-tetrahydrocannabinol(Δ⁹-THC) in hempseed oil by gel permeation chromatograph-high performance liquid chromatography(GPC-HPLC) method was developed. Methods Samples were extracted with cyclohexane and ethyl acetate and the extract was purified by GPC,then separated by Agilent Eclipse XDB-C₁₈ column(150 mm×4.6 mm,3 μm).The acetonitrile-water was used as mobile phase,and quantified by secondary tube array detector and external standard method. Results The linear correlation coefficient (r) of this method was above 0.999 in the concentration range of 0-500 μg/L.Δ⁹-THC had a limit of detection(LOD) of 0.05 mg/kg and the limit of quantity(LOQ) of 0.17 mg/kg. Recoveries were between 84.6% and 101.8% and the relative standard deviation were within 3.2%-4.7%(n=6). With the actual samples tested, Δ⁹-THC content in 10 different brands of hempseed oil ranges from 0.40-5.82 mg/kg. Conclusion The results showed that the method had good stability and high sensitivity,and was suitable for determination of Δ⁹-THC in hempseed oil.