The fatty acid, all $cis-{Delta}^{5,11,14}-C_{20:3}$, in the Gingko nuts oils, was isolated and, purified by urea-adduct method, silver ion silica gel chromatography and HPLC equipped with reversed phase ${mu}-Bondapak$ $C_{18}$ column. Its structural elucidation was conducted by IR and $^1H$-, $^{13}C$-NMR technique. The fatty acid composition of seed oils mainly consists of linoleic acid(37.73%), vaccenic acid(18.30%), oleic acid(15.18%), palmitic acid(3.37%), palmitoleic acid(3.37%) and ${Delta}^5$ NMDB fatty acids(8.50%) in which all $cis-{Delta}^{5,11,14}-C_{20:2}$ predominates.