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This paper reports the synthesis of hierarchical aluminosilicate inorganic polymers (also known as geopolymers) containing both Bronsted and Lewis acid sites that function as a new class of heterogeneous solid acid catalysts. The geopolymers were synthesised from a naturally occurring clay mineral by an energy-efficiently and ecologically friendly process. Their catalytic performance was evaluated in a model liquid phase Friedel-Crafts alkylation of relatively large substituted benzenes (alkylation of toluene, anisole, p -xylene and mesitylene with benzyl chloride). The influence of the geopolymer starting composition on the acidity and porosity of the synthesised catalysts was studied and the impact of post-synthetic demetallation on their catalytic performance was investigated. The geopolymer-based catalysts achieved high catalytic activity which was superior to H Y zeolite under identical reaction conditions. These results suggest that geopolymers have considerable potential as cost efficient, readily synthesised and environmentally friendly heterogeneous solid catalysts for fine chemical applications.