Abstract: Process for the synthesis of aromatic alkylated hydrocarbons with a saturated alkyl chain including at least four carbon atoms, according to which an aromatic hydrocarbon, replaced by an alkyl group with a short saturated chain comprising one to three carbon atoms, is made to react with an olefin in the presence of a catalyst made up of at least one alkaline metal or a alkaline metal hydride impregnated on an alumina support. The process is characterised by the fact that the catalyst is prepared in the reaction medium in the presence of the aromatic hydrocarbon with a short alkyl chain by mixing anhydrous alumina with the alkaline metal hydride or with the alkaline metal, and then the olefin is introduced in order to start the reaction.