In this paper the bituminous water proof mortar, which has been used between the bricks in the Achaemenes monument of Tall-e-Ajori in Persepolis, has been analyzed by different instrumental chemical analysis methods, such as Fourier transform infrared spectroscopy (FTIR), X ray diffraction (XRD and X ray florescence spectroscopies (XRF). Moreover, due to identifying the chemical structure and explanation the degradation processes during thousand years of remaining inburial environment, the classical extraction by organic solvents and optical microscopy studies were also done. According to classical extraction test results, the physical state of the bituminous water proof mortar is a duple mixture that include organic and inorganic parts, where the characteristic of the material is actually a natural asphalt. The organic part of this bituminous mixture was analyzed by FT-IR method for identifying the main organic functional groups such as alkanes and aromatic molecules, XRD analysis determined the presence of inorganic phases such as Calcite, Anhydrite, Feldespar (Ca), Quartz and Dolomite, and the result of XRF analysis determined weight percent of CaO, SO3, SiO2, Al2O3, Fe2O3 and MgO. The degradation processes during thousands of years in the burial environment have developed the age-hardening reactions which decrease the saturated molecules concentration such as oils and resins in bituminous mixture, and caused the enhanced fragility and brittleness in the structure of the material. So, the results obtained clarifies the importance of conservation programming and climate controlling for optimum preserving of the bituminous mixture mortars in the Achaemenes monument remains of Tall-e-Ajori in persepolis.