Abstract: This invention relates to an improvement in the process for preparation of 2-(amylbenzoyl)benzoic acid containing a high percentage of 2-(t-amylbenzoyl)benzoic acid. More particularly it relates to a process for preparation of 2-(amylbenozyl)benzoic acid wherein said 2-(amylbenzoyl)benzoic acid is prepared by reacting t-amylbenzene with phthalic anhydride in the presence of Lewis acid, characterized by that 2-(amylbenzoyl)benzoic acid containing a high percentage of 2-(t-amylbenzoyl)benzoic acid is produced by suppressing the undesirable isomerization reaction of the amyl radical by applying one of the means selected from the group consisting of the means of introducing an inert gas into the reaction system and the means of reducing the pressure of the reaction system. 2-(Amylbenzoyl)benzoic acid is a compound useful as the starting material of preparation of 2-amylanthraquinone which is an effective organic catalyst in the manufacture of hydrogen peroxide.