1,2-Disubstitued benzimidazoles were selective synthesized in excellent yields by the condensation of o-phenylenediamine with aromatic aldehydes under mechanically activated solvent-free conditions in ball mill using FeCl3•6H2O as the catalyst. Structures of products were characterized by 1H NMR, 13C NMR and HRMS. The optimum conditions were given: n (FeCl3•6H2O) : n (o-phenylenediamine) : n (aldehydes) = 0.25 : 1 : 2 and the ball mill was run with a rotational speed of 400 r/min for 2 h. The reaction was carried out without solvent and just needed a simple work-up procedure. This mild and eco-friendly method had the potential for facile preparation of benzimidazole derivatives.