In this work, the microwave dielectric properties of Cu and PEO based composite sheets are studied in the X-band. The desired composites sheets (thickness ~ 250 μm) are prepared via solution casting method, one of the best methods for sheet preparation. Various characterization techniques including the X-ray diffraction and Scanning Electron Microscopy are used to analyze the presence and uniform dispersion of Cu particles into polyethylene oxide (PEO) matrix. Vector Network Analyzer is employed to obtain the scattering parameters (S21/S11), which are then used to extract the dielectric permittivity of the samples using cavity perturbation technique in the X-band of microwave frequency. The real and imaginary parts (dielectric constant and dielectric loss) of the complex permittivity of synthesized composite sheets are found to be increased with the addition of copper contents (10, 20, and 30 wt %). This enhancement of the dielectric properties in the X-band of microwave frequency may be attributed to the interfacial polarization mechanism. Copyright © VBRI Press.