The core/shell-type ZnO nanosphere/CdS nanorod and ZnO nanosphere/CdS nanoparticle composites have been selectively prepared through a simple ultrasound-assisted solution phase conversion process using monodispersed ZnO nanospheres as a starting reactant and in situ template. The formation mechanism of the products is closely connected with the sonochemical effect of ultrasonic irradiation. The photoluminescence and electrogenerated chemiluminescence properties of the as-prepared core/shell structures were investigated.