Abstract: The microcellular epoxy resin was prepared by the solid-state batch foaming technique with supercritical CO₂ as a physical-blowing agent. The preparation processes of microcellular epoxy resin were studied by SEM and DSC, mechanical properties and dielectric properties of the epoxy resin before and after foaming were analyzed. The results show that when the pre-curing degree of epoxy resin sheets is 75%-85%, the gas concentration will reach 5.11%-5.43%, the gas saturation time will be 48 h, and the cells are closely packed and the size is uniform. With the improvement of foaming temperature and extension of foaming time, the average cell diameter of the microcellular epoxy resin will gradually enlarge and the cell density will decrease. When the pre-curing degree of epoxy resin sheets reaches 75%, the foaming temperature is 120 ℃ and the foaming time is 10 s, the average cell diameter of microcellular epoxy resin will be 10.6 μm and cell density will be 1.03×10⁹ cells/cm³. And the cells are uniform and compact spheres or polygons structure. Compared with materials without foaming, the elongation at break and impact strength of the microcellular epoxy resin increase by 43% and 39% respectively. The dielectric constant and the dielectric loss decreases by 42% and 50% respectively.