This thesis shows the characterization and identification of microplastic waste found in the sediment of Bačvice beach in Split and in the estuary of the river Neretva. Sampling and separation of samples was carried out by the Institute of Oceanography and Fisheries in Split. The samples were delivered to the address of the Faculty of Chemistry and Technology in Split, where further analysis were performed. Characterization of microplastics was performed on 228 specimens from the Bačvice location in Split and 32 from the Neretva. Specimens were visually analyzed and sorted into categories according to shape, defined by the DeFishGear protocol: filaments, films, fragments, granules, pellets and foams, after which their color and transparency were determined. The mass of the individual specimens was determined using an analytical balance while the area and maximum dimension were determined using a Digimizer image processing program. Identification of the type of microplastic was performed by FTIR spectroscopy and differential scanning calorimetry. A total of 40 specimens from the Bačvice site and 32 from the Neretva site were identified. Others were too small to analyze with these techniques. The most common category is fragments. Samples are mostly opaque, white in color. Most samples, by size, belong to microplastics (particles < 5 mm in diameter). The most common type of polymeric material in the total sample is polypropylene, followed by polyethylene (high and low density) and polystyrene. The obtained results indicate that microplastic waste exists in the sediment of the Croatian beaches, which for the most part probably originates from improperly discarded disposable packaging.