Determination of  stability limits, mineralogical changes and  thermal reaction of serpentine minerals are very important for the  investigation of magmatism, mechanism and depth of  plates of subduction. During the subduction process, serpentine (Lizardite) minerals will release their water due to thermal reactions. This dehydration can play an important role in volcanism processes related to the subduction. In this study, serpentine minerals (Lizardite) collected from the Neyriz Ophiolite Complex (NOC) were dehydrated under the constant atmospheric pressure. These mineralogical changes were determined by X-Ray diffraction and DTA-TG analyses methods. This study shows natural lizardites that heated for about one hour is stable up to 550°C. Dehydration reactions on lizardite started at approximately between 100 to 150°C and dehydroxilation reactions started at approximately 550-690°C. As a result of thermal reaction, the decomposition of lizardite will take place and then changes in to olivine (forsterite).  Crystallization of olivine (forsterite) will start at 600°C. This mineral is stable up to 700^oC and then crystallization of enstatite will start at 700°C. During this dehydration and crystallization reaction, amorphous processes will start at 600°C and some amount water and silica will release.