Copper-containing single-source precursors for preparation of SiCuCN-based ceramic nanocomposites were successfully synthesized for the first time using polysilazane, copper acetate monohydrate and 2-aminoethanol via nucleophilic substitution reaction at the Si centers of polysilazane. The synthesis process, polymer-to-ceramic transformation and high-temperature microstructural evolution of the prepared ceramics were characterized. Dielectric properties and electromagnetic wave (EMW) absorbing performance of the ceramics were investigated as well. The results show that the polymer-to-ceramic transformation finishes at ca.900℃, and Cu nanoparticles are homogeneous distributed in the SiCN matrix, forming a SiCN/Cu nanocomposite.