The aim of this study is to compare the effects of NaOH addition in the decomposition of dihydrobenzenes(catechol and hydroquinone) using supercritical water(SCW) and supercritical water oxidation(SCWO) conditions. Experiments were performed using four sets of conditions, which were in the presence and absence of NaOH in both SCW and SCWO conditions. Under the experimental conditions, the addition of NaOH accelerated the decomposition of catechol and hydroquinone in both the conditions. Several intermediates were identified by performing GC/MS analysis from SCWO of catechol and hydroquinone, and in particular, a large quantity of 1,4-benzoquinone were detected from SCWO of hydroquinone, which is known as an probable inhibitor to hinder the production of CO2 after hydroquinone oxidation. The addition of NaOH to catechol and hydroquinone oxidation reduced the generation of these intermediates including 1,4-benzoquinone, however the effects of the NaOH addition in SCW were the similar as compare to those of SCWO. Further, the addition of NaOH increased the production of CO2 and CH4 in both the conditions. These results revealed that the effects of NaOH on the decomposition of catechol and hydroquinone using SCWO are not negligible. Therefore, its effects on the decomposition of other organic compounds under SCWO conditions should be estimated for determining optimized operating conditions and reactor designs.