An environmentally benign, highly efficient one-pot four-component synthesis of highly functionalized imidazole derivatives using different aldehydes, substituted amines, benzil, and ammonium acetate in the presence of biodegradable and highly efficient catalyst chitosan-SO3H were described. Chitosan-SO3H was found to be a heterogeneous acidic catalyst which allowed easy recovery of the catalyst. Use of microwave irradiation along with chitosan-SO3H for the synthesis of imidazole derivatives makes this protocol green. Moreover, excellent yields, shorter reaction time, chromatography-free purification, and elimination of environmentally hazardous solvents are other advantages of this protocol which leads to sustainability.