A process for preparing a hydrocarbon conversion catalyst, which process comprises: (a) preparing an aqueous mixture containing aluminum sulfate and having a pH in the range of from 1.2 to 4.0; (b) adding alkali metal aluminate to the mixture obtained in step (a) to increase the pH of the mixture to within the range of from 7.2 to 10; (c) adding aluminum sulfate to the mixture obtained in step (b) to lower the pH of the mixture to within the range of from 3.1 to 5.1; (d) adding alkali metal silicate to the mixture obtained in step (c) to increase the pH of the mixture to within the range of from 7.2 to 8.5, wherein the final steps of the preparation process are (v) adding aluminum sulfate to the mixture obtained in a process comprising steps (a)-(d) to lower the pH of the mixture to within the range of from 2.5 to 7.5; (w) adding alkali metal silicate to the mixture obtained in step (v) to increase the pH of the mixture, (x) adding to the mixture obtained in step (w) (i) alkali metal aluminate to change the pH of the mixture to of from 7.8 to 11 and (ii) aluminum sulfate to change the pH of the mixture to within the range of from 3 to 7.5, wherein step (i) can precede or succeed step (ii), (y) treating the mixture obtained in step (x) with an alkaline solution having a pH of from 8 to 11, to precipitate silica-alumina solids and separate from the solution, (z) recovering the precipitate solid from the mixture obtained in step (y) to obtain a silica-alumina composition containing of from 30 to 70 %wt silica and of from 70 to 30 %wt of alumina, and having a surface area of from 320 m 2 /g to 450 m 2 /g as measured by the BET method according to ASTM test D3663-03, and subsequently shaping the silica-alumina composition obtained, and calcining the shaped composition in an oxygen containing atmosphere at a calcination temperature of from 500 to 900°C, and compositing the shaped silica-alumina composition with one or more metals or metal compounds which metals have been selected from the group consisting of Group VIB and Group VIII metals to obtain a hydrocarbon conversion catalyst. (a) preparing an aqueous mixture containing aluminum sulfate and having a pH in the range of from 1.2 to 4.0; (b) adding alkali metal aluminate to the mixture obtained in step (a) to increase the pH of the mixture to within the range of from 7.2 to 10; (c) adding aluminum sulfate to the mixture obtained in step (b) to lower the pH of the mixture to within the range of from 3.1 to 5.1; (d) adding alkali metal silicate to the mixture obtained in step (c) to increase the pH of the mixture to within the range of from 7.2 to 8.5, (v) adding aluminum sulfate to the mixture obtained in a process comprising steps (a)-(d) to lower the pH of the mixture to within the range of from 2.5 to 7.5; (w) adding alkali metal silicate to the mixture obtained in step (v) to increase the pH of the mixture, (x) adding to the mixture obtained in step (w) (i) alkali metal aluminate to change the pH of the mixture to of from 7.8 to 11 and (ii) aluminum sulfate to change the pH of the mixture to within the range of from 3 to 7.5, wherein step (i) can precede or succeed step (ii), (y) treating the mixture obtained in step (x) with an alkaline solution having a pH of from 8 to 11, to precipitate silica-alumina solids and separate from the solution, (z) recovering the precipitate solid from the mixture obtained in step (y) to obtain a silica-alumina composition containing of from 30 to 70 %wt silica and of from 70 to 30 %wt of alumina, and having a surface area of from 320 m 2 /g to 450 m 2 /g as measured by the BET method according to ASTM test D3663-03, calcining the shaped composition in an oxygen containing atmosphere at a calcination temperature of from 500 to 900°C, and compositing the shaped silica-alumina composition with one or more metals or metal compounds which metals have been selected from the group consisting of Group VIB and Group VIII metals to obtain a hydrocarbon conversion catalyst.