Due to the widespread occurrence and the potential threat to the environment, plastic materials are currently a growing problem of environmental protection in the world. Plastics whit dimensions not exceeding 5 mm are called microplastics. One of the main sources of microplastics in the aquatic environment are municipal wastewater treatment plants. The paper presents the results of research on the presence of microplastics in leachate from sludge processing at a large municipal wastewater treatment plant. The leachate was divided into the leachate produced in the processes of sludge thickening and dewatering. The analysis of the isolated microplastics included a physical analysis, which focuses on determining size, shape, and color of the isolated material. The next step was the chemical identification of the microplastic, where the type of polymer of the tested material was confirmed by means of Attenuated Total Reflection Fourier Transform Infrared. Among the isolated microplastic particles, almost a half was identified as fragments, and a smaller amount was confirmed for the presence of foil, fibers, foams and granules. The identified particles were plastic materials, including polypropylene, polyethylene, polystyrene or poly(terephthalate). Based on the results of the conducted research, the mass of microplastics in leachate was characterized and determined.