The effect of Lewis and Bronsted acid modification on the catalytic behaviour of SnO2 was studied. Modified AlCl3, FeCl3, ZnCl2 and H2SO4 were used for this purpose, Catalytic activity was tested for Friedel-Crafts alkylation, acylation and Pechmann condensation, It was observed that the alkylation activity of SnO2 was improved upon treatment with Lewis acids and Bronsted acids. However the acylation activity was observed only when SnO2 was treated with H2SO4. Moderate improvement in the activity for Pechmann condensation reaction was : observed in the case of all the modified catalysts. It was inferred that this method of modification resulted in an increase in acid strength as well as acidity of the parent oxide catalyst,