Polystyrene nanometer-sized particles supported alkaline 1-propyl imidazolium ionic liquids catalysts (nano-PS-CH2-[pIM][B]) were prepared and characterized by FT-IR, SEM, TG/DTA, BET and particle size distribution analysis. The results suggested that ionic liquids were successfully loaded on the surface of polymer carriers by covalent bond with high alkali amount. It showed excellent catalytic activities for Knoevenagel condensation especially in aqueous phase, which much higher than that of NaOH and micro-PS-CH2-[pIM][B]. It will be expected for the potential application of organic reactions in aqueous phase.