Vacuum pressure assisted gel-casting and reaction sintering were applied to fabrication of Φ200 and Φ500mm ultra-lightweight SiC mirrors with the area densities of 9.17 kg/m2 and 10.8 kg/m2 respectively. The main properties of the SiC mirrors were tested. The results show that the green bodies of the SiC mirrors have no macroscopic defects due to its pouring in a vacuum environment. The mirror materials have high flexural strength (335 MPa) and fracture toughness (4.5 MPa·m12) because of the fine SiC particles. The metallographic structures of the mirror materials do not show the directional alignment of SiC particles, which means the mirror materials possess a high isotropy ratio, in which the relative deviation of Coefficient of Thermal Expansion(CTE) is less than 3%, and the relative deviation of modulus reaches 1.3%. After polishing, the surface profile accuracy (RMS) of the mirror is 0.043λ (λ=632.8 nm), and the toughness is better than 5 nm. These results demonstrate that the ultra-lightweight SiC mirrors fabricated by vacuum-assisted gel-casting and reaction sintering have excellent performance, and are suitable for fabrication of the mirrors of space cameras.