Silica-included tungstophosphoric acid and its Cs salt, zinc ion-exchanged smectite clays, and montmorillonite K10 could be effectively applied as insoluble, readily recoverable solid acid catalysts to the hydrolysis of ethyl acetate, liquid-phase Friedel-Crafts reactions, and the synthesis of alkylporphyrin derivatives, respectively. They are expected to be alternatives to the environmentally problematic homogenous acid catalysts such as sulfuric acid, aluminum chloride, and boron trifluoride.