One of the key technologies for next generation space telescope with a large-scale reflector is a material having high specific strength, high specific stiffness, low coefficient of thermal expansion and high coefficient of thermal conductivity. Several candidates such as fused silica, beryllium, silicon carbide and carbon fiber reinforced composites have been evaluated. Pitch-based carbon fiber reinforced SiC composites were developed for the SPICA space telescope mirror to comply with such requirements. Mechanical performance such as bending stiffness, bending strength and fracture toughness was significantly improved. Evaluation procedures of thermal expansion and thermal conductivity behavior at cryogenic temperatures (as low as 4.5K) were established and excellent performance for the SPICA mirror was demonstrated.