In this article, an efficient, simple and environmentally friendly approach to the synthesis of diacetals (diketals) pentaerythritol using SO3H-functionalized ionic liquids (ILs) as catalysts was reported. The Ils show high catalytic activity and reusability with good to excellent yields of the desired products. Hammer method has been used to determine the acidity order of these ionic liquids and the results are consistent with the catalytic activities observed in acetalization reaction. Maximum product yield of 93% was observed on using[PSPy][Otf]as catalyst and it can be reused at least 8 times without obvious activity loss.