Thailand experiences plastic waste and microplastic contamination (MPs) caused by waste disposal and leachate treatment systems. MPs often escaped from the leachate treatment. This research collected leachate and sludge samples from the leachate treatment system. This research aimed to determine the amount and characteristics of Microplastics (MPs) and assess the effectiveness of microplastics in the leachate treatment system. The research also aimed to determine the amount of heavy metals deposited on microplastics and assess the exposure to heavy metals from the soil surrounding the leachate utilization. The microplastic samples were analyzed using a Fourier Transform Infrared Spectrometer (FTIR) to determine the composition and the type of plastic. The heavy metals on microplastics and in the open dumpsite soil were analyzed using Inductively Coupled Plasma Optical Emission (ICP-OES). The study found that the efficiency of removing microplastics in the leachate treatment system was 77.55%. The microplastic content in all leachate sampling locations was 105±11 pieces/l, and microplastics were found at a concentration of 65±3 pieces/kg in the sludge. The detected size of microplastics ranged from 20 to 10 micrometers and fragment shapes were the most common. The composition of the most transparent microplastics was examined, with polyethylene found to be the most prevalent at 30.55%, followed by Polyester at 17.77%. Zinc was the most common heavy metal found, while Cadmium was not detected in either the wastewater or sludge samples on microplastics. Most MPs removed from the leachate accumulate in the sludge, which may pose a risk to the environment. Therefore, a way to deal with the sludge is needed to reduce the contamination of microplastics (MPs).