Although microplastics are transported from land-based sources to aquatic environments there is currently little knowledge about its fate from land sources to coastal marine waters. In addition to riverine discharges, storm drainages from urban settlements might contribute an important source of microplastics. Mar del Plata city harbor (Buenos Aires, Argentina) holds the most important fishing fleet and shipyard facility in Argentina. Although that several contaminants have been reported in sediments from this area, the occurrence of microplastic has not be studied. The aim of this study was to evaluate the spatial distribution of microplastic in subtidal sediments (5-12 mt deep) from 4 sites in Mar del Plata's harbor, differing in their distance to “Del Barco” creek stormwater outlet. Microplastic content was determined (n:3 per site) by a density floating method using a zinc chloride (ZnCl2) solution (δ1.65). Mean total abundance of microplastics ranged from 1600 to 8700 items per kg d.w. Sediments from areas near to the discharge showed significantly higher abundances (p