Effects of types and amount of catalysts,hydrogen pressure,and kinds of vegetable oils on the formation of conjugated linoleic acids (CLA) isomers,and the effects of hydrogen temperature and agitation rate with a selective Ni catalyst on the formation of total CLA were studied during hydrogenation process.CLA isomers were identified by a silver ion-impregnated HPLC and 100m cyano-capillary column GC.