A series of ignition experiments using electric sparks are made to investigate the explosion characteristics of gaseous ozone with a concentration up to 60 vol%. The results show that the lower explosion limit of ozone diluted in oxygen at room temperature and atmospheric pressure is about 10 vol%. Partial decomposition of ozone in the ignition vessel is observed in the range from 10 to 12 vol%,and ozone with a concentration of more than 12, vol% can cause an explosive chain decomposition and convert to oxygen completely. The lower explosion limit shifts to higher concentration with decreasing initial pressure. For instance, at 100 Torr the lower limit is 25 vol%, Explosion pressure ratio Is proportional to ozone concentration. For 40 vol% ozone, the ratio is 8, Besides. detonation was observed at ozone concentration above 40 vol% in our experiment. Moreover, we have proved that carbon dioxide has a weak restraint effect on ozone explosion, As a result, adding carbon dioxide to 70 vol% into an ozone-oxygen mixture can raise the lower explosion limit to 12 vol%.