A plasma process was applied for synthesis of phenol(C₆H₅OH) as final product from benzene(C₆H₆) or toluene (CH₃C₆H₅). Phenol formed from both the materials, but its yield was different. The yield was higher from benzene than from toluene. Greater similarity of benzene to phenol and simpler in chemical composition and structure compared with toluene account for the higher yield from the former material than the latter. And the higher yield was due to less formation of impurities from benzene and more impurities such as benzyl alcohol and cresols from toluene. In the state of plasma water molecules gave off OH radicals accompanied by H and O radicals through homolytic fission of the molecules by bombardment action of thermal electrons. The OH radicals the outside of what is totally covered by the huge plus phase of Lowest Unoccupied Molecular Orbital (LUMO) and approached the bulky breadth of plus phase of Highest Occupied Molecular Orbital (HOMO) situated around the C-H bond of benzene and to that of the C-C bond of toluene molecules. The breadth is caused by excitation in stretching vibrations of C-H in the structure of benzene and of C-C in toluene. The excitation is induced by thermal energy of the plasma process, following to a phenomenon that the energy level of LUMO decreases and the level of HOMO increases for both benzene and toluene molecules. The phenomenon results in closer energy levels of HOMO and LUMO, making the molecules easily flow into the situation of orbital electron excitation caused by photo irradiation and/or collision with thermal electrons probably from the metal electrode used for an electric discharge in the state of plasma. The molecules in the orbital electron excited state are so chemically active that they easily reacted with OH from the water, resulting in quick formation of phenol under the relevant plasma generated in this experiment.