Photon emission (phE) during fracture was investigated on glass-like carbon, pyrolytic graphite, polycrystalline graphite, and carbon fiber reinforced composites (C/C composites). The C/C composites were heat treated at 1000, 1500, and 2000 degrees C. The specimen was fractured by three-point bending and the resulting phE was measured at atmospheric pressure, 10(-3) and 10(-6) Pa. The phE was not observed on any samples at atmospheric pressure, whereas it occurred on the glass-like carbon and C/C composites at 10(-3) and 10(-6) Pa. The phE intensity at 10(-3) Pa was higher than that at 10(-6) Pa. This study revealed that the phE on the carbon materials depended on their crystal structure and surrounding gas pressure. The gas pressure dependence suggests that the phE resulted from gas discharge.