A continuous two step O3/H2O2 oxidation system, in which the waste gas from the former reactor was reused in the latter step with an ejector, was established for the purpose of wastewater reclamation in electronics industries. ORP monitor was combined into the system to obtain the optimum ratio of H2O2 to O3 by automatically adjusting the dosage of H2O2, and ion exchange resin was used for removing organic acids formed during oxidation. The effectiveness of the O3/H2O2 oxidation system for TOC removal was investigated under various conditions by using IPA, DMSO, and NMP as model substances. The optimum H2O2/O3 for oxidizing IPA was in a range above 0.15, and it increased with the increase of O3 dose. A sudden drop of ORP from ca. 800 mV to a little more than 200 mV was observed when H2O2/O3 was approaching the optimum point from the lower end. An ORP between 250 mV and 300 mV or 800 mV and 900 mV was proper for H2O2/O3 control. The treatability of the model substances was in an order of IPA << DMSO < NMP, being consistent with the magnitude of the energy of the highest occupied molecular orbital (epsilon HOMO). The two step treatment system developed in this study was found to be more efficient than the conventional single step system. With the help of H2O2 dosing control and two step treatment using waste O3, the system could save about 40% O3 in comparison with the conventional O3/H2O2 oxidation process.