A method for preparing aluminum sulfate which comprises subjecting sulfuric acid and aluminum hydroxide to reaction, wherein the reaction is advanced in the presence of at least one member selected from the group consisting of nitric acid and a peroxide. An industrial composition comprising aluminum sulfate. By the method of the present invention, aluminum sulfate can be efficiently and commercially advantageously prepared. Further, the industrial composition of the present invention can be advantageously used in various industrial fields as, for example, a waste water treatment agent, a paper sizing agent, a tanning agent for hides, a clarifying agent for fats and oils, or a catalyst for industrial use.