Under ultrasound activation, imidazole was condensed with ethyl acrylate using two basic clays (Li+ and Cs+ montmorillonites). The clay catalysts were characterized by chemical analyses, nitrogen adsorption isotherms, and X-ray diffraction. Under sonochemical conditions N-substituted imidazole can be obtained with a high activity and selectivity. The conversion increases with the basicity of the clays and the ultrasonic exposition time. The yield presents a maximum for 0.1 g of Cs+ montmorillonite after 60 min of sonication.