Awaruite was found in serpentinized peridotites from the Mineoka district, southern Boso Peninsula. The mineral occurs invariably in serpentinized parts of the rocks, indicating that it was formed in the course of serpentinization. Heazlewoodite and native copper were formed also in association with awaruite during serpentinization. Chemical analysis of the awaruite yields the formula: Ni_2.26 Fe. Native copper associated with heazlewoodite contains about 5 weight percent nickel. The occurrence of awaruite suggests that oxygen fugacity of fluid being responsible to serpentinization was lowered at least locally down to 10^-42 bar during serpentinization. The low oxygen fugacity of fluid was resulted from reaction between fluid and fayalite component of olivine producing magnetite and serpentine minerals.