In this paper we show the feature of the microwave heated oxygen plasma torch which we designed and apply it to the conversion method of metal chloride wastes in a pyrochemical reprocessing into oxides. For this purpose oxygenation experiments of several typical metal chlorides were carried out by using this plasma device and thermodynamic equilibrium diagrams of each metal chloride and oxygen system were calculated. Consequently, it was found that our oxygen plasma has a possibility to realize such a oxygenation reaction, the equilibrium diagrams can predict the oxygenation characteristics of metal chlorides by oxygen plasma and the chlorides have conversion characteristics according to their oxygenation difficulties. Finally, we classified chlorides into three categories by predictions from the calculated thermodynamic equilibrium diagrams.