The trans fatty acids in vegetable oils were determined according to the national standard GB/T 22110-2008 Determination of trans fatty acids in food-Gas chromatographic method , and the uncertainty was assessed. The results showed that the trans fatty acids in vegetable oils could be determined accurately by the laboratory,and the extended relative uncertainty of the result was 4.2%(K=2); the repeatability of the result by gas chromatography was the largest percentage of the total uncertainty, which provide technical reference for such projects and controlling the accuracy in the future.