Sefidkuh Granitoid is located west of Nehbandan (South Khorasan Province) east of Lut Block. Compositionally, this granitoid ranges from granite (monzo and synogranite), to granodiorite and tonalite. It has microgranular felsic enclaves with minerals similar to the host body. Major minerals are quartz, plagioclase, microcline, orthoclase, and biotite which were analyzed using electron probe micro-analyzer (EPMA) for thermometry and mineral chemistry studies. Plagioclases in granites are mainly andesine and sometimes albite and in enclaves they are andesine. Anortite content in plagioclase decreases from core to rim, which shows normal zoning of plagioclase. Alkali feldspars in enclaves are sanidine compared to orthoclase in granite. Biotites in granite are primary ferroan and formed in low fo₂ and under, reduced condition while biotites in enclaves are primery magnesian and formed in high fo₂ and oxidized conditions. Thermometry based on feldspar and biotite compositions yielded about 500-750 ˚C for granite and 650-950 ˚C for enclaves. Mineral chemistry studies indicate that granite (peraluminous magma) and enclaves are derived from a calc-alkaline magma belonging to active continental margin setting.