In this work, we studies the effect of size and thickness variation on the opticalrnproperties of a system that consists of spherical ZnO@Cu and ZnO@Au core-shellrncomposite nanostructures embedded in a dielectric host matrix. The effective dielectricrnfunction, refractive index, and absorbance of the composite nanostructures arerndetermined using the Maxwell-Garnett effective medium theory within the frameworkrnof the electrostatic approximation. The numerical simulation using nanoinclusions ofrnradii 30 nm shows interesting behavior in the optical responses of the ensemble. Inrnparticular, it is shown that for different values of volume fraction and filling factorrnthe refractive index and optical absorbance of the ensemble exhibited two setsrnof resonance peaks; the first set located around 515 nm and 490 nm and the secondrnset found above 635 nm and 605 nm spectral regions for a system of ZnO@Curnand ZnO@Au nanoparticles, respectively. These peaks are attributed to the surfacernplasmon resonance of copper and gold at the core@metal and metal@host-matrix interface.rnMoreover, when the Cu and Au shell thickness is increased, the observedrnresonance peaks are enhanced; accompanied with slight red shifts for the first setrnof peaks and a blue shifts for the second set of peaks. In brief, it is seen that thernoptical properties of spherical ZnO@Cu and ZnO@Au core-shell nanoinclusions embeddedrnin vacuum can be tuned by varying the shell thickness, filling factor, and/orrnvolume fraction of the nanocomposites. The results obtained may be used in variousrnapplications such as sensors and nano-optoelectronics devices in optimizing materialrnparameters to the desired values.