Abstract: To match the thermal expansion coefficient of copper foil, the thermal expansion properties of SiO₂-TiO₂ ceramic filled PTFE microwave substrate composites were investigated. SiO₂ together with TiO₂ were added to PTFE matrix by the wet process. The influences of the SiO₂-TiO₂/PTFE composite density, ceramic particle size and volume fraction of ceramic filler on the thermal expansion coefficient(CTE)of the SiO₂-TiO₂/PTFE composites were investigated. The results show that as the volume fraction of SiO₂ increases from 0 to 40%(TiO₂: 34%-26%), the linear expansion coefficient of the composites decreases from 50.13×10^-6K^-1 to 10.03×10^-6 K^-1. The decrease of ceramic particle size and density of composites results in the decrease of the CTE. According to the calculation of CTE with ROM, Turner and Kerner models, the experimental values show better matching with the theoretically predicted values using ROM and Kerner models. Whereas, promotion of the difference between experimental value and the predicted value by Turner model is along with PTFE volume fraction increasing.