Improvement of the sulfated zirconia catalysts ( SZN) was studied by adding different amounts of alumina as follows: 17.5, 29.8, 45.9, and 56wt %. Even though, alumina, is expect to promote higher specific area and increase the amount of acid sites, stability of the zirconia tetragonal phase, the active zirconia phase of the SZN catalyst isisomerization reaction was obtained for catalysts containing between 17.5, and 29.8wt % of alumina, which reflects the promotional effect of alumina. On the contrary, a strong reduction of this reaction rate is observed when higher amounts of alumina are added to the catalyst, which indicates the dilution effect of alumina.