An efficient method for Knoevenagel condensation of aromatic aldehyde with malononitrile and ethyl cyanoacetate catalyzed by inexpensive and ecofriendly solid catalyst ZnO at room temperature is developed. The reaction was carried out under solvent free condition and in aqueous medium. In addition to this un catalyzed reaction in aqueous medium is reported for comparison.. The alkenes derivatives are obtained in excellent yields in aqueous medium in presence of ZnO catalyst. The potential advantage of the catalyst is alkenes derivatives are obtained in excellent yields in short duration under mild condition using malononitrile. The reaction between aromatic aldehyde and ethyl cyanoacetate was slow and requires longer time for completion. The catalyst is thermally stable, easy to recover, high product yield and can be efficiently recycled without any pretreatment.