The Middle Miocene Niyasar granitoid complex is located in west of Kashan and in the Urumieh – Dokhtar magmatic belt. Based on petrographic studies, the Niyasar complex is composed of tonalite, quartz-diorite and diorite intrusive rocks. These rocks are mainly composed of quartz, plagioclase, amphibole, biotite and K-feldspar. The amphiboles belonge to calcic group and vary in composiotion from magnesiohornblende to actinolite which is an indicative of I-type granitoids. The composition of plagioclase ranges from oligoclase to bytonite in the tonalites, albite to andesine in the quartz-diorite and oligoclase to bytonite in the diorites. Barometric studies exhibit that the hornblende pressure crystallization was 1-2 Kbar which is equivalent to 3.8-7.5 Km depth of crystallization. Hornblende-plagioclase and feldspar thermometry in the Niyasar complex show 706-756 ˚C as equilibrium temperature of minerals. Oxygen fugacity estimation, suggests that the Niyasar intrusive crystallized from highly oxidized magmas in a convergent boundary setting.