The liquid phase alkylation of resorcinol with tert.-butyl alcohol was carried out over HZSM-5, HY, HM, MCM-41. alumina, montmorillonite-K10 and modified montmorillonite-K10 (mont.-K10). The major products of this reaction on these catalysts were 4-tert.-butyl resorcinol and 4,6-di-tert.-butyl resorcinol. Unmodified montmorillonite-K10 shows a very low conversion compared to modified montmorillonite. The conversion in terms of catalytic activity increases in the order modified mont.-K10 much greater than HZSM-5 > HY > HM > MCM-41 > Al2O3 > mont.-K10. The activity and selectivity differences between the catalysts are explained based on their physical properties and acidity differences. The study brings out the significantly high butylation activity of modified montmorillonite-K10 compared to zeolite and oxide catalysts.