This invention relates to a new conjugated linoleic acids, a process for preparation thereof and method of use. Thus this invention is concerned with the preparation and purification of conjugated linoleic acids from materials rich in alpha or gamma linoleic acids. The reaction produces a mixture containing a 1:1 ratio of 9Z, 11E, 15Z-octadecatrienoic acid and 9Z, 13E, 15Z-octadecatrieonic acid. The mixture can be purified up to 90% by liquid chromatography, crystallization or urea crystallization. The mixture of 1:1 9Z, 11E, 15Z-octadecatrienoic acid and 9Z, 13E, 15E, 15Z-octadecatrienoic acid have anticancerous activities.