Serpentinites in Chungnam area are mainly composed of serpentines. Serpentines of olivine origin consist of pseudomorphs of olivines and show mesh textureen closed with magnetites along the boundaries of serpentine crystals. In some serpentinites, serpentinization is occurred in crystal boundaries and/or cracks of olivines and pyroxenes which are relict minerals of dunite and harzburgite. On the process from olivine to serpentine, Mg ions are greatly decreased and Si ions are greatly increased, and $Fe^{2+};and;Fe^{3+}$ ions are a little decreased. But, on the process from pyroxene to serpentine, Si ions are greatly decreased and Mg ions are greatly increased. Magnetites around the serpentine crystals were formed from the iron which had been left out through this serpentinization process of olivine. Serpentinization from the original rocks such as dunite and harzburgite in Chungnam area was occurred by various waters affected after formation of original rock, and particularly by metamorphic water in the metamorphic conditions ranging from green schist facies to granulite facies through amphibolite facies.