A series of azo dyes were efficiently synthesized by mixing aromatic amines and NaNO 2 in the presence of nano silica supported boron trifluoride (nano BF 3 ·SiO 2 ) and then diazo coupling with 1-naphthol under solvent-free conditions at room temperature. The present methodology has proven to be simple, rapid, environmentally benign, green, and cost-effective compared with previous synthetic methods. Also, by using this procedure, aryl diazonium salts supported on nano BF 3 ·SiO 2 were very stable to be kept at room temperature for several months without any special conditions.