The research of heavy metals contents in soil and leaves of Sessile oak (Quercus petraea (Matt.)Liebl.). Moreover, the paper presents the analysis of the stand state on the Avala Mountain. The Avala area ishigh-grade protected natural resource located on the territory of Belgrade (Serbia) and its regime of exploitationand protection is clearly defined. It is assumed that the human factor is the primary cause of degradation of theprotected areas of Avala. Therefore, the current inadequate stand composition and the impact of trafficpollution can be considered the decisive causes of degradation on mountain, as a natural area under specialprotection. Determining the degree of loading of soil and plants with heavy metals and the analysis of standconditions of such valuable protected areas such as the area of Avala, are of great importance, based on theresults obtained, to take appropriate timely precautionary measures, in order to preserve, improve natureconservation, the environment in general, and especially health conditions. The research of the contents ofheavy metals (Pb, Ni, Fe, Zn i Mn) in soil showed the load of soil especially with Pb and Ni. In third locactionthe concentration of Ni (amounting to 7.0 μg/g) in the plants leaves is significantly higher which indicates theexistance of chemical contamination of soil, before all, with this pollutant. The measured concentrations of allexamined heavy metals (Pb, Ni, Zn, Mn and Fe) in the leaves of Sessile oak on Avala fall within the maximumallowed values in accordance with the legal regulations in Serbia.