A novel method for condensation reaction of indan- 1,3-dione with various aldehydes which are efficiently catalyzed by a task-specific ionic liquid, 2-hydroxyethylammonium formate, to provide the corresponding 2-arylidenindane-1,3-diones has been developed. This green, low-cost, high-yield, and fast reaction takes

place at room temperature without the use of any solvent and catalyst. A plausible reaction mechanism that involves ionic liquidassisted activation is also discussed. This work is the first report of ionic liquids as a reaction medium and catalyst for the synthesis of 2-arylidenindane-1,3-diones.