A series of NiO-ZrO₂ catalysts were prepared by coprecipitation from the mixed aqueous solution of nickel chloride-zirconium oxychloride, and were modified with acids, H₂SO₄, H₃PO₄ and H3B03. It was found that the NiO-ZrO₂ catalyst containing 25 mole percent of nickel oxide and evacuated at 400 for 1.5 hr showed maximum catalytic activities for 1-butene isomerization and cthylene dimerization. The catalytic activities for both isomerization and dimerization were correlated with the acid strengths of the catalysts. The isomerization activity of 1-butene ran parallel with the dimerization activity of ethylene, although the isomerization took place on relatively weak acid sites as compared with they dimerization.