Landfills leachates are one of the most polluted waste waters and they may have a significantly bad impact on human health and environment. That is why the processing is needed and lowering their concentration on acceptable levels for the environment. The regulations from environment bodies only give restrictions based on design of landfills themselves and discharging leachate. Currently, there is no universal procedure for all leachates. Specific solutions are needed for every type of leachate water, depending on its characteristics. The presence of high concentrations of ammoniacal nitrogen (NH3-N) in landfill leachate during long periods of time is one of the main problems that landfills are faced with. For removal of NH3-N, a couple of technologies are used, they include: precipitation, coagulation, anaerobic removal of ammonia, membrane technologies, stripping etc. In this thesis, the physical-chemical process of chemical precipitation is used with the asistance of hydrated lime, which was combined with the procedure of carbonization, with goal of removing ammoniacal nitrogen. The removal of ammoniacal nitrogen after this process was 100% successful, and there was a significant lowering of other values critical for safely discharging processed leachate into the environment following the given law regulations. Testing with the usage of CO2 and sulfuric acid for the purpose of regulating pH values, the importance of the given method was visible. Three mechanisms of removing NH3-N were given: adsorbing into precipitate, transforming into urea and its precipitation, and lastly volatilization into ammonia gas, which was the most important one for achieving this results.