An efficient method for the synthesis of 14-alkyl or aryl 14H-dibenzo[a j]xanthene derivatives by the reaction of β-naphthol, and aldehydes in the presence of a catalytic amount of bismuth(III) chloride (BiCl3) under solvent-free conditions at 110℃ is described. Aliphatic and aromatic aldehydes were used in the reaction and in all cases the desired products were synthesized successfully. This reaction was studied under different temperatures; the maximum yield was obtained in a short reaction period at 110℃. The method offers the advantages of high yields, short reaction times, simplicity and easy workup compared to the conventional method of syntheses.