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For the first time, we employed the halogen-free deep eutectic solvent (DES) into the Knoevenagel condensation between aromatic aldehydes and active methylene compounds at room temperature. The DESs [3Im:PTSA] and [4Im:PTSA] were prepared by imidazole (Im) and p-tol-uenesulfonic acid (PTSA), which were experimentally screened from a series of organic acids with imidazole. a, b-Unsaturated carbonyl compounds were obtained in good to excellent yields under solvent-free conditions with fast reaction rate. These two DESs can be reused for multiple times with no loss of catalytic activity.