Gachsaran Formation is the most important cap rock of hydrocarbon reservoir in Iran and has important deposits of salt, sulfur and gypsum. A section of Gachsaran formation (Early to Middle Miocene) in south-east of zagros area, west of Bandar-e-Abbas province, was studied from sedimentary geology view. Gachsaran Formation in studied section, with 310 m thickness consist of Chehel, Champeh and Mol members and consist of gypsum/anhydrite, limestone and marl lithofacies. fourty-four samples has been taken from this section for microscopic examinations and X Ray Diffraction analysis.This research showed that evaporative deposits in Kuh-e-Namaki Khamir section, contain of gypsum, anhydrite, dolomite and halite minerals and marl deposits contain of palygorskite, dolomite and calcite minerals and carbonate deposits contain of dolomite and calcite minerals. The mineralogical composition and lithological characteristics, confirm that Gachsaran Formation in the study area has deposited in lagoonal to Sabkha environment with warm and dry climate and limit regress and progress of sea.