The Caspian Sea is the largest enclosed aquatic ecosystem in the world. The combinations of the toxic pollutants with microplastics endanger the Caspian Sea ecosystem. In this work, the distribution of microplastics was studied in surface waters and southern Caspian Sea coasts sediments. The samples were collected from eight stations, including the Tonakabon, Chalos, Nowshahr, Noor, Mahmood Abad, Babolsar, Sari, and Neka coasts. The average concentrations of microplastics in the coastal waters and sediments were 34,490 particles per km2 and 210 particles per kg, respectively. Isolated microplastics were characterized using ATR-FTIR and energy dispersive X-ray (EDS) techniques. The samples exhibited a strong carbon peak in the EDS spectra, which was screened as microplastic particles. The microplastics were mainly fragments and foams and identified as polyethylene, polypropylene, and polystyrene by means of ATR-FTIR spectra. This is the first study to determine the distribution of microplastics in southern Caspian coastal regions.