The largest problem of domestic anaerobic digestion was low digestion efficiency. The cause of the problem would be low organic matters input, low mixing efficiency and refractory sludge etc.. In this study, in order to solve these sludge problems, ozone solubilization was used. Results of this study, SCODcr concentration was reported to have increased average 355.5% (100.7 to 680.0%) by ozone solubilization. In addition, the sludge solubilization efficiency was investigated to average 77.2 (51.8 to 96.0) %, and SCODcr/TCODcr ratio of digested sludge (before solubilization) was investigated to average 0.02 (0.01 to 0.04); and SCODcr/TCODcr ratio of solubilized sludge (after solubilization) was investigated to average 0.19 (0.09 to 0.70). Biochemical methane potential (BMP) results showed that microbial activity was decreased by the ozone solubilization and methane generation rate (reaction rate k) was decreased to 3.02-fold. However, this study`s results showed that methane production was increased to 1.52-fold and the methane generation rate (k) was improved to 1.44-fold in mixed sludge (mixing of digested and solubilized sludge) than only the digested sludge.