A series of 5-arylidenethiazolidine-2,4-diones was synthesized by the Knoevenagel condensation of thiazolidine-2,4-dione with aromatic aldehydes with alkaline ionic liquid 1-butyl-3-methylimidazolium hydroxide ([bmim]OH) as dual solvent and catalyst. This method provides many advantages such as being environmentally benign, simple work-up, short reaction times, obtaining in good to excellent yields, and the reusability of ionic liquid. 5-Arylidenethiazolidine-2,4-diones constitute an important class of chemically, biologically and pharmaceutically significant compounds. 1,2 For example, they are key intermediates for the synthesis of anti-diabetic drugs such as troglitazone, pioglitazone, rosiglitazone, englitazone. 3 The conventional synthesis of 5-arylidenethiazolidine-2,4-diones involves the Knoevenagel condensation of aromatic aldehydes with thiazolidine-2,4-dione catalyzed by organic base or salt in refluxing volatile organic solvent such as benzene, 1 toluene, 4 acetic acid, 4,5 ethanol, 2,6,7 etc. However, these reactions require long reaction times (16-24 h), tedious work-up procedures, and sometimes only moderate yields obtained.Recently, some methods have been developed such as facilitated by solid base, 8 ionic liquids, 9 solid condensation, 10 or MW irradiation. 11,12 Although the condensation reactions could be completed in short times, these methods have their own disadvantages yet, such as using unamiable organic solvent, added catalyst required, difficult to prepare in large scale, etc. Considering the importance of 5-arylidenethiazolidine-2,4-diones, we think it is still significant to develop more facile and practical