Currently, some of the plastic waste, which accounts for a large proportion of municipal solid waste (MSW) in Korea, is treated through incineration. However, waste plastic is not completely removed by incineration treatment, and it is sometimes found in the form of microplastics (MPs) in incineration ash. Therefore, MSW incineration facilities are classified as one of the sources of microplastics. It can be expected that the MPs found in the incineration ash that have undergone a high-temperature treatment process would exhibit different characteristics from those detected in other environmental media. Therefore, in this study, nine municipal solid waste incineration facilities of different sizes were selected, and the amount and characteristics of MPs contained in incineration bottom ash (BA) generated in each facility were investigated. In addition, changes in characteristics before and after combustion were confirmed using plastic that is mainly used in everyday life. Consequently, ND ~ 158.0 MPs/kg-BA were detected in incineration ash in small- and medium-sized incineration facilities and up to 106.6 MPs/kg-BA in incineration ash in large incineration facilities. Most of the detected MPs were black, and it was difficult to determine that it was plastic with the naked eyes. In addition, combustion experiments of plastics were conducted to confirm that the characteristics of the material before and after combustion changed significantly. Results revealed that special attention was required in the detection of microplastics in incineration ash as a modified form of spectrum different from that of raw materials.