Alkyl- or aryl-14H-dibenzo[a,j]xanthene derivatives are synthesized efficiently by the reaction of beta-naphthol and aliphatic and aromatic aldehydes in the presence of KAl(SO4)2 x 12 H2O (alum) under aqueous condition at 100 degrees C. Different types of aromatic and aliphatic aldehydes are used in the reaction and in all cases the products synthesized successfully. Several solvents were examined for this reaction; however, in terms of reaction yield and time, water was found to be the optimum solvent.