In this study, effects of rare earth oxide CeO2 and Y2O3 on the structure and properties of glass-diamond composites were systematically researched. The thermal analysis of the borosilicate glass was performed by TG-DSC curves. Phase composition of the glass-diamond composites was analyzed by XRD. SEM images showed the microstructure of the composites. Thermal properties of the composites were characterized by thermal conductivity and coefficient of thermal expansion. Bending strength was measured to explain the mechanical properties. Results showed that the addition of CeO2 and Y2O3 improved the mechanical and thermal properties of the glass-diamond composites and CeO2/Y2O3 compound additive had greater impacts on the composites than single additive. When the content of CeO2/Y2O3 additive reached 4 wt % (1.07 vol %), the thermal conductivity and bending strength of the glass-diamond composites increased by 69.77% and 35.13%, respectively.