Sodium dihydrogen phosphate (NaH2PO4) efficiently catalyzes the condensation reaction of benzil,aldehydes,amines and ammonium acetate in a four-component reaction under solvent-free conditions.The reaction proceeds rapidly and affords the corresponding tetra-substituted imidazoles in high yields.Also an efficient route was developed for the synthesis of tri-substituted imidazoles from condensation of benzil,aldehydes and ammonium acetate using NaH2PO4.