SbCl3–Al2O3 is proposed as a highly efficient, cost effective and reusable Lewis acid catalyst for the selective synthesis of 1,2-disubstituted benzimidazoles from o-phenylenediamine and aromatic aldehydes in an excellent yield (86-95%) using microwave (MW) irradiation under solvent-free conditions. The present methodology shows some specific advantages such as mildness, short reaction times and enhanced selectivity under solvent-free conditions.