A process for fabricating three-dimensional photonic crystals composed of SiO2-TiO2-based ceramics with a diamond structure was investigated. An epoxy structure having an inverse diamond configuration was fabricated by stereolithography, a rapid prototyping method. The epoxy structure was infiltrated with a ceramic slurry and then cold isostatically pressed. After sintering at 670degreesC for 5 h in air, the epoxy was burned off, leaving behind the desired structure of a ceramic photonic crystal. The calculated band diagram indicated that an absolute photonic band gap for all wave vectors existed. The measurement of transmission in the (100) direction from 10 to 20 GHz showed that a complete band gap formed at about 14.7-18.5 GHz. The magnitude of the maximum attenuation was as large as 30 dB at 17 GHz, which indicated that the fabricated structure worked well as a photonic crystal.