Microplastics are minute pieces of plastic with diameters ranging from a few micrometers to a couple of millimeters. In recent years, microplastics have become a global marine environmental issue since they may adversely affect coastal and marine ecosystems and potentially harm the health of human beings. In light of this issue, Japan is investigating the distribution of microplastics and the amount of harmful chemical substances such as PCB that are adsorbed to such microplastics in the coastal and offshore areas of Japan and a wide area spanning from Japan to the South Pole. In addition, the government is calling on businesses to stop using microbeads in personal care products such as scrubs.*1 Microplastics are classified into primary microplastics and secondary microplastics. Primary microplastics are manufactured as materials for use in scrubs and industrial abrasives and are often made of polyethylene (PE) or polypropylene (PP). Secondary microplastics refer to plastics that have been broken down from larger debris into pieces with a diameter of 5 mm or less due to external factors such as ultraviolet radiation*2 and the types of such plastics are various. A Fourier transform infrared spectrophotometer (FTIR) is suited to the analysis of microplastics since FTIRs are optimal for the qualitative analysis of organic compounds. In cases where the sample is minute and no larger than 100 μm, the use of an infrared microscope is effective. This article introduces example analyses of primary and secondary microplastics utilizing an infrared microscope.