A process for the preparation of alkyltetralins which comprises feeding an alkenylbenzene into a reaction zone continuing a fixed bed of an acidic cyclization catalyst, and cyclizing it in the liquid phase at a temperature not higher than about 300.degree. C., characterized in that:I. at least a part of the reaction mixture containing the unreacted alkenylbenzene, which has been withdrawn from said reaction zone and in which the conversion of alkenylbenzene is below the intended final conversion, is cooled, and at least a part of the cooled reaction product in an amount sufficient to adjust the temperature of the reaction zone to not higher than about 300.degree. C. is recycled to said reaction zone, andIi. the remainder of the reaction product is led into another reaction zone containing a fixed bed of acidic cyclization catalyst, and without the aforesaid recycling, further cyclized in the liquid phase until the intended final conversion is attained.