Friedel-Crafts alkylation of benzene with benzyl chloride was studied by using organochloroaluminate ionic liquids as Lewis acid catalyst. The reaction was performed in the temperature range of 40 to 70 ℃ at benzene/benzyl chloride=17, where selectivity to diphenylmethane was high. The optimum AlCl3/BMIC ratio of the ionic liquid for the benzylation reaction was 2. Superior performance was obtained with butyl group constituting the cationic species of the ionic liquid. Stirring speed had a major impact on catalytic activity of the BMIC-AlCl3 ionic liquid; benzyl chloride conversion decreased substantially from 98 to 68% as stirring speed was reduced from 900 to 500 rpm, and eventually no reaction took place at 200 rpm. BMIC-AlCl3 ionic liquid was more active than Fe-MCM-41 at the expense of a small drop in selectivity but still higher than 96% selectivity was obtained. The ionic liquid could be easily recovered after phase separation. The performance of BMIC-AlCl3 ionic liquid was maintained after the second run with 97.4% conversion and 95.6% selectivity, but a sudden drop in activity was observed after the third run with only 26.8% conversion.