A series of nanocomposites, SiCN/A3S2 ceramics, were prepared by hot-pressing method. The nanometer SiCN powder is characterized of high dielectric dissipation. The dielectric properties of the SiCN/A3S2 nanocomposites were investigated. XRD and SEM were conducted to study the phases and microstructure of the nanocomposites. Compared with the pure A3S2 ceramic, the grain size in the nanocomposites is reduced due to the addition of nanometer SiCN powder. The relative densities of the nanocomposites are also lower than that of the pure A3S2 ceramic. Both the real and imaginary parts of the complex permittivity of nanocomposites in X band increase as the content of SCN powder in the samples rises obviously. When the contents of SiCN powder in samples are same, the real and imaginary parts of the samples vary with the sintering temperature. The tanδ of the nanocomposites reduces from 1.9 to 1.4 when sintering temperature increases from 1450OC to 1650 OC. SAED pattern reveals that structure of the SiCN in SiCN/ A3S2 sintered at higher temperatures tend to crystallize. The real, imaginary parts and dissipation factor of the nanocomposites sintered at higher temperature is lower than those sintered at 1450 °C.