The Maksan granitoid is located in the south margin of Lut block, and southeastern Iran. It composed of granite, granodiorite, monzodiorite, quartz monzodiorite, diorite and gabbro. Compostions of biotite from different rock types of Maksan granitoid, i. e., granite, granodiorite, monzodiorite (Quartz monzodiorite), diorite and gabbro in SE of Iran have been documented by electron microprobe. Biotite chemical composition is Mg-biotite and based on their TiO₂, MgO, MnO, FeO and Al^IV content, they are primary magmatic biotites. They have formed in relatively high oxygen fugacity environment and show calc-alkaline characteristic (I-type) that correspond with tectono-magmatic characteristics related to subduction environments. Biotite mineral chemistry shows that magma constitution has low to moderate contamination with continental crust.