Catalysts have been found which are effective in the isomerization of vegetable oils to conjugated forms. These catalysts include active surface materials such as diatomaceous earth and carbon black, nickel on kieselguhr, and nickel on carbon black. Since these catalysts are neutral, they do not split ester linkages, and no further chemical treatment of the isomerized oil is required. The nickel-on-carbon catalyst is the most effective, particularly when it is prepared by reduction of a suitable nickel salt on Nuchar XXX or Nuchar C-190. When 6 to 8% of reduced catalyst is heated for 6 hours at 170°C. with alkalirefined soybean or linseed oil, 30 to 34% conjugation is obtained. A sample of catalyst may be used to isomerize five to ten hatches of oil before its activity is lost. The treated oils dry in substantially less time than the untreated, and the water and alkali resistances of their films are appreciably improved. A process is proposed for conjugating vegetable oils by the nickel-on-carbon catalyst.