World has been faced with serious problems of water pollution. Recently, conventional chemical treatment has been replaced by a water treatment system using plasma. In this study, a method for decomposing organic compound by spraying solution directly as mist into reactive plasma was investigated using a newly developed mist-flow plasma reactor. The plasma reactor is a tube made of Teflon with a thickness of 0.5 mm has an inner mesh electrode made of stainless and an outer grounded electrode made of copper. Non-thermal plasma is generated by dielectric barrier discharge (DBD) at the inner wall of a tube. An atomized solution containing micro-sized droplets was introduced into the plasma reactor and treated by ozone, free radicals and ultraviolet rays. Dissolved chemical species such as H_2O_2, reactive oxidation species and O_3 are measured as liquid properties. The decomposition characteristics of this method were experimentally clarified through decolorization of methylene blue solution. The methylene blue solution is about 100 % decomposed by only one treatment under certain operating conditions. In addition, a water treatment method using aerosol plasma is compared with a activated air microbubble jet treatment.