The nano-crystalline sulfated-zirconia catalysts, prepared by one-step as well as two-step sol-gel technique, showed excellent catalytic activity with a high substrate to catalyst weight ratio for the synthesis of 7-substituted 4-methyl coumarins via solvent free Pechmann reaction. The m-amino phenol was found to be more reactive than m-hydroxy phenol. The catalyst results 100% conversion of m-amino phenol with similar to 100% selectivity of 7-amino 4-methyl cournarin at 110 degrees C within 2 min. For 7-hydroxy 4-methyl coumarin, 94% yield was obtained after 3 h at 170 degrees C with phenol to catalyst weight ratio of 80. Slow kinetics was observed in polar nitrobenzene as well as in non-polar toluene for both cournarin derivatives, due to the slow bulk diffusion of reactant molecules in presence of solvent. The solvent free microwave assisted synthesis seems advantageous way to synthesize the hydroxy derivative resulting excellent yield (99%) in much lesser time (15 min) at lower temperature (150 degrees C) as compared to thermal heating. The use of very small catalytic amount of sulfated-zirconia catalyst for the synthesis of coumarins and the reusability of the catalyst after simple activation for several times with similar catalytic activity are novel properties of the catalyst. (c) 2007 Elsevier B.V. All rights reserved.