Microplastics represent an exacerbating form of pollution that has spread through the environment even to most isolated natural habitats. This is caused by multiplicity of potential sources as well as the characteristics of particles that enable their spread through the environment in various ways. Also, a growing number of field and laboratory research provide insights into the potentially harmful effects of plastic micro-particles on natural habitats as well as organisms and ultimately entire communities that inhabit them. The aim of this study was to conduct a quantitative analysis of microplastics from the surface layers of the sea in harbors of Zadar and Šibenik by using a 300 µm mesh net. Project results showed that the average concentrations of microplastics in seawater in two urban areas were 0,80 particles/m³. Regarding the physical characteristics, the most abundant particles were in the form of fibers (51%), followed by fragments (33%), mostly under one millimeter in size (51,7%), transparent (48%) and blue (16%) in color. This corresponds to the most represented type of particles from global research. Fibrous and fragmented structures are usually the characteristic of the secondary type of microplastics, therefore its predominance points to submarine wastewater discharges, decomposition of discarded waste, fishing activities and transport of particles from urban areas by wind or runoff as the main sources of pollution in this case.The methods used in this study proved to be adequate and also accessible for sampling, however, there is a need for progress through the implementation of more precise methods and more frequent sampling over a longer time period for a more complete insight into the spatio-temporal fluctuations of microplastics in marine ecosystems.