Abstarct: The study area (~90 km2) is located in 3 km south west of Mayamey (60 km to the east of Shahrood City) in Semnan province of Iran and Central Iran structural zone. With attention to field,petrographic and geochemical studies,granitoidic rocks of south west Mayamey consist of four groups:alkali feldspar granites,syeno-monzo granites,granodiorites and microdioritic dykes.The some of the granitoidic rocks are deformated and indicated submagmatic fabrics. These microstructures include of fractures filled by quartz and feldspar and is formatted in final steps of crystallization, in presence of remaning melt and indicate high-temperature deformation.Also, in the south margin of the granitoidic body of the study area,is observated mylonitic and deformated rocks. Variation diagram trends of major and trace elements of samples are indication of some gaps in rock groups and probably distinct source for these rocks.The studied samples show Sr,Ta,P,Nb,Ti depletion and enrichment in Rb,Th,U,Pb,K. The chondrite normalized REE patterns are characterized by enrichment in LREE, in comparison with HFSE. High Rb,Th,K and low Sr,P,Ti and Nb values suggest some crustal contamination during magmatic evolution and/or correlated with subduction zone magmatism. Geochemically these rocks are peraluminous to slightly mextaluminous, typical of I and S type granites and belong to high-K calc-alkaline series. The abundance of incompatible elements and the negative Eu anomaly indicated that the granitoidic rocks of Mayamey are originated from partial melting of lower crust. In such a setting, the melts of partial melting of oceanic plate, emplaced into the lower crust and provide the heat required for crustal anatexis. Fractional crystallization of the melts can generate the granitoidic rocks represent in Mayamey area. Tectonic setting diagrams indicate that this intrusion belong to a continental arc granites(CAG) and probably in duration "Middle Cimmerian" events, the subduction of Neotethys oceanic plates to the beneath of continental plate of Central Iran, lead to generation of calc-alkaline andesitic magmas.Then, these magmas emplaced into the lower crust and provide the heat required for crustal anatexis. Fractional crystallization of the melts can generate the granitoidic rocks.