The Sikhoran Mafic–Ultramafic complex is located in the Sanandaj – Sirjan structural zone. The complex consists of two main rock units: the lower harzburgite - porphyroclastic dunite unit and the upper layered gabbroic cumulate unit. The microstructures and geochemical evidences provided a better understanding of serpentinization and emplacement processes of this complex. The petrographic studies revealed three microstructural types including: High T solid slate microstructure, which occurs mainly in NE of the porphyroclastic dunite unit, Low T solid state microstructure in NE and central parts of dunites – harzburgites, and finally mylonitic - sub mylonitic microstructures, which mainly found in harzburgite unit. Moreover, the vein microstructures outcrop in the mylonitic- submylonitic zone. The veins have been formed by two processes of crack seal and dissolution. Deformations have occurred mainly around the Ashin fault. Hydrothermal fluids have resulted in serpentinization and mobility of iron and also other elements from ferromagnesian minerals of primary peridotites. Serpentinites show the SiO2amountof 38.8-41.7 wt%, and also depletion of Al2O3 and CaO. The depletion in CaO (0.3-0.9 wt %) and Al2O3 (0.1- 1.3) and enrichment in Cr and Ni indicate the depleted parent rock of mantle harzburgite or dunite, and a supra- subduction zone in Cr - TiO2 diagram.