PURPOSE: To produce an alkylated aromatic compound in a state separated from a catalyst without using a large-scale apparatus by carrying out the reaction using a fine grain solid catalyst.

CONSTITUTION: This process for the production of an alkylated aromatic compound comprises the following steps. (1) A step to react an aromatic compound with an olefin in the presence of a fine grain solid catalyst to obtain a reaction liquid containing an alkylated aromatic compound, (2) a step to separate the reaction liquid into a reaction liquid containing the alkylated aromatic compound and a reaction liquid containing the fine grain solid catalyst and (3) a step to separate the alkylated aromatic compound from the reaction liquid containing the alkylated aromatic compound.