Abstarct: Challu granitoid pluton is located at South East of Damghan and the Northern part of Central Iran structural zone. The pluton geochemically is I –type, calc-alkaline and mextaluminous in nature and belongs to the volcanic arc (VAG) granitoids. In this area, there are voluminous Eocene volcanic rocks with composition of andesite – trachy andesite and andesitic basalt which are the host rocks of iron mineralization and mextasomatism. Intrusion of the pluton into volcanic and volcanic - sedimentary rocks and the resultant hydrothermal fluids has been caused alteration and mineralization. baxsed on field and petrography investigations, the Challu intrusive body compositionally includes of monzodiorite and quartz diorite. The pluton has porphyroidic and trachytoidic textures and include of plagioclase, orthoclase, biotite, amphibole and pyroxene. Overall, two different alteration phases is identified. The first phase is propylitic alteration and is characterized by epidote and chlorite mineral assemblages. This type of alteration is more widespread and is observed in monzodiorite unit. The second phase is argillic alteration and occurred locally near to the major fracture zone. There are fine grain enclaves in the rim of monzodioritic unit. Angular xenoliths from carbonated tuffaceous and host rocks also are observed. Present study investigates the emplacement mechanism of the Challu intrusive body using by the anisotropy of magnetic susceptibility (AMS). Following results are extracted from the magnetic parameters studies. - The average measured magnetic susceptibility (Km) is obtained 28872 μSI for monzodiorite and 21487 μSI for quartzdiorite. The pluton belongs to the ferromagnetic granites due to having km> 500 μSI, then the magnetite is the most carrier of magnetic susceptibility. - Circulation of hydrothermal fluids throughout the intrusive body has been caused the main mineral compositions variation and changed the magnetic properties of minerals original. Magnitude of measured magnetic susceptibility in the intrusion shows different variations depending on the type of alteration, so it obviously decreases from fresh rock to the rock that subjected into propylitic and argillic alterations, respectively. This result shows how magnitude of magnetic susceptibility decreases during alteration due to removal or reducing in the size of magnetite or converting that to hematite. - Magmatic microstructure is predominant in Challu granitoid body. - The field observations, petrographic and fabrics magnetic studies (the lineation and foliation pattern, magnetic parameters such as T, K1, K2, K3, Km and P%) indicate that the mention pluton have been emplaced in the two phases with two different mechanisms. The monzodioritic unit with dominant porphyroidic texture and NE lineation and foliation patterns parallel to the margin has emplaced in one tensional gash at one dexteral shera zone. Simultaneously or shortly after that, quartzdiorite unit has been emplaced as dykes along the fracture p -type. The magnetic fabric patterns and also oblate ellipsoid magnetic shape and trachytoidic texture in the wall confirm with revers fabric at dikes. The oriantation of plagioclase laths indicate magma flow direction.