Sulfonic acid functionalized diatomite afforded diatomite-SO3H as an efficient heterogeneous solid acid nanoporous. The resulting immobilized catalysts have been successfully used in the synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes under solvent free conditions. This procedure has a lot of advantages such as very easy reaction conditions, recyclable heterogeneous acidic catalyst, natural catalyst, absence of any tedious workup or purification and much milder method. The corresponding products have been obtained in excellent yields, high purity and short reaction times. (C) 2014 Elsevier B.V. All rights reserved.