Ultrasonic atomization technique is used for the preparation of nanostructured ZnO powders. These powders were characterized using XRD, SEM, TEM and elemental analysis using EDAX. Furthermore this nanostructured ZnO powder is used to prepared thick films using screen-printing techniques. Thick film is used as sensor to test the conventional gas and simulant of highly toxic chemical warfare agents. It was observed from XRD and TEM that the powder consisted of nanocrystallites with sizes less than 20 nm. It was confirmed from TEM analysis that the crystallites were nearly spherical in shape. The thick film sensor showed maximum response to NH3 and DMMP.