A three-dimensional photonic crystal with a diamond structure made of epoxy lattices incorporating TiO2-SiO2 composite ceramics particles were fabricated by stereolithography. The transmission spectra of microwaves with TE10 mode through the photonic crystal showed the existence of a complete photonic band gap in the frequency range of 14.3-15.8GHz. An air cavity defect with a rectangular shape was introduced into the photonic crystal by removing three or five unit cells aligned in the diamond structure. The transmission amplitude of microwave through each defect structure showed the existence of a resonant mode inside the photonic band gap. A planar waveguide with the diamond structure, which contains an air cavity layer, was also formed by using stereolithography. It showed a transmission of a resonant mode at 15.4GHz.