Linoleic acid was heated in the presence or absence of water in the temperature range of 200 to 260°C using a pressure-resistant batch reactor to examine the possibility of its conversion to conjugated isomers. The conversion occurred at very low yields, and the major products were the c9, t11 and t10, c12 conjugated linoleic acids. The t10, c12 isomer seemed to be produced more than the c9, t11, and the ratio of the isomers did not depend on both the temperature and the ratio of linoleic acid to water. When a dilute potassium hydroxide was used as the aqueous solution, the yield of the conjugated isomers was lower than that of the isomers in the mixture of linoleic acid with distilled water.