Magnesium oxide nanopartticels in average size between 35-120 nm were prepared by sonochemistry method. Synthesis of polyhydroquinoline derivatives using MgO nanoparticles from the reaction of dimedone, benzaldehyde, ethyl acetoacetate and ammonium acetate under solvent-free conditions is reported. Easy handling, reusability, thermal stability and non-toxicity of the catalyst make the present protocol as an eco-friendly and economically acceptable method for synthesis of these heterocycles.