The middle Jurassic Shir-Kuh granitic batholith in Central Iran intruded to the sandstones and shales of Nayband-Shemshak Formation. The batholith consists of three main granodioritic, monzogranitic and leucogranitic units. The granodiorites composed of plagioclase, quartz and biotite and is limited to the northern margin of the batholith. The monzogranites which made the dominant unit range from relatively mafic (cordierite-bearing) to felsic (muscovite-rich) rocks. The leucogranites character-ized by white color and absence of opaque minerals consist mainly of quartz, K-feldspar, and sodic plagioclase and located along the northwestern margin. Separation of restite from initial melt composition appears to have been an effective differentiation process in the formation of more mafic rocks of the batholith. The relatively felsic was formed due to fractional crystallization. The boundary between the two types is at about 70% SiO2.