The alkylation of the oil extracted from an FCC slurry with 1-octadecene, as catalyzed by the ionic liquid Et3NHCl.2AlCl(3), was investigated in this work. The reaction conditions (such as catalyst dosage, molar ratio of extracted oil to 1octadecene, reaction temperature, and reaction time) were optimized through measurements of the conversion ratio of reactants and the chemical structure of the alkylated product. Under the optimal reaction conditions, the conversion ratios of extracted oil and 1-octadecene reached up to 78.6% and 79.3%, respectively, simultaneously yielding good selectivity to the monoalkylated product with an average molecular mass of 470. The experimental results indicate that Et3NHCl-2AlCl(3) not only has a good alkylation catalytic activity for grafting long alkyl chains onto PAHs but also exhibits excellent recyclability, retaining 95% of its initial activity after eight reuses. This study suggests a promising application of the extracted oil from FCC slurries as a raw material for producing high-quality petroleum sulfonates.