PURPOSE: To produce an alkylaromatic compound in high reaction selectivity using a decreased amount of catalyst based on the produced alkylaromatic compound.

CONSTITUTION: A 2-4C olefin, an aromatic compound and a Friedel-Crafts catalyst are introduced into a 1st reaction zone maintained at 90-140°C to effect alkylation reaction. The molar ratio of olefin/aromatic compound is 0.2-1.0 and the amount of the catalyst is 0.0003-0.01mol based on l mol of the olefin. The reaction product containing a polyalkylaromatic compound and discharged from the 1st reaction zone is introduced together with the recycling Friedel- Crafts catalyst into a 2nd reaction zone and subjected to transalkylation reaction at 90-140°C. The Friedel-Crafts catalyst is separated from the reaction product of the 2nd reaction zone and recycled to the 2nd reaction zone. The reaction product free from the catalyst is distilled to separate the aromatic compound and the polyalkylaromatic compound. The former compound is recycled through the 1st reaction zone, the latter compound is recycled through the 2nd reaction zone and the alkylaromatic compound is recovered from the reaction product.