The specific municipal waste (bottom ash and stabilized sewage sludge) can be applied for rehabilitation of post-industrial areas and landfill sites. The mixture of this waste in a 1:1 ratio is a mineral - organic composite used as material for rehabilitation. The multi-stage procedure of sequential extraction forms the preferred tool applied in the analysis of the potential hazard that is formed by the waste. The paper presents the analysis of heavy metal contents in particular fractions of composite separated by sequential extraction according to Tessier’s procedure. The sequential extraction analysis was carried out in order to identify the particular forms and fractions forming the total content of a given metal and assess the mobility of elements into the environment. The five forms of heavy metals were identified: exchangeable, carbonate, oxide, organic and residual. Cadmium and zinc occurred primarily in the carbonate associations. The highest content of lead and copper was determined in organic fraction. Chromium and nickel occurred primarily in residual fraction. The analysis of heavy metals release using basic leaching test according to PN-EN 12457-2 was also carried out. The study demonstrated low leachability of heavy metals. Due to the very small ratio of heavy metal forms that are water soluble, the waste was considered to be safe to the soil and water environment.