The present invention relates to processes of regenerating Ni catalysts which had been used in a hydrogenation of unsaturated fatty oil or petroleum resin, which comprise separating the Ni-extracted solution and support by extracting the pretreated Ni catalysts with an acid, preparing support-containing solution by burning the separated support in the flow of air or oxygen diluted with nitrogen at the temperature of 300.degree. to 800.degree. C. for 5 to 15 hours and adding deionized water to the support, preparing a catalyst precursor by dropping the Ni-extracted solution and the mixed solution of a basic compound and a compound with free oxygen in the support-containing solution during agitation so as to keep PH of the solution at 9 to 13, whereby nickel oxide precipitates on the support, carrying out a step consisting of aging, washing, filtering and drying the catalyst precursor, and stabilizing the dried catalyst precursor by reducing with hydrogen and passing in nitrogen diluted with oxygen or an organic material.