A rapid analytical method for trans-fatty acid determination using a single capillary column was developed, and an isothermal condition for separating cis/trans-isomers with 30- to 60-m columns depending on the contents of the trans-fatty acids was established. Under the established conditions, analysis of trans-fatty acids was completed in 20 min for non-hydrogenated oils low in trans-fatty acids and in 40 min for hydrogenated oils rich in trans-fatty acids. The results were virtually the same as those obtained by the AOCS official method with a 100-m column. By correcting with molecular weights of fatty acid methyl esters and free fatty acids, it was confirmed that the analytical data were the same as those obtained by quantitative analysis using an internal standard. It is anticipated that this proposed method can be applied in a similar way to the AOCS official method, particularly in quality control processes.