This study systematically investigates the characteristic degradation behaviors of dimethylsulfoxide (DMSO) by the streamer corona discharge process (SCDP) in water. The analysis of the oxidized intermediates of DMSO shows that hydroxyl radical (OH) is the main oxidant responsible for the degradation of DMSO in the SCDP. The various experiments on the degradation and mineralization of DMSO, and the effect of the OH scavenger suggest that the SCDP produces locally concentrated OHs in and around the plasma channel. This explanation was also supported by the formation of H2O2 and the effect of the OH scavenger on the H2O2 production rate in the SCDP. Based on the kinetic data for the degradation of DMSO and the production of H2O2 in the SCDP, the volume of the active region in which the OHs are concentrated, and the effective concentration of OH in that region were estimated to be 0.21 μl and 5.0 × 10⁻³ M, respectively. This level of OH concentration in the SCDP is approximately 10⁷–10⁹ times higher than that generated in ordinary advanced oxidation processes using OH. The ramifications of the results obtained in this study on successful water treatment using the SCDP are also discussed.