This study was performed to determine the possibility of sludge treatment by ozone for reducing the sludge production in sewage treatment. To evaluate the characteristics of the release of organic matters and nutrient from sludge degradation by ozone, SCOD, SBOD/TCOD, T-N and T-P were analyzed. From the results, we concluded that the concentration of soluble organic matters(SCOD) was increased with reaction time. Also, The concentration of T-N and T-P were increased with time like as organic matters. Quantities of released SCOD, SBOD, T-N and T-P by ozonization were 0.038g, 0.058 g, 0.011 g, 0.012 g per g MLSS, respectively.