The presence of microplastics in rivers remains an unanswered question in many parts of the world. The research aimed to determine the presence of microplastics (MP) in river sediments of the lower basins and mouths of the Lurín and Chillón rivers. For monitoring, 4 stations were established for each river (E.CL1, E.CL2, E.CL3, E.DL4 and E.CCH1, E.CCH2, E.CCH3, E.DCH4), located from the lower basin to the estuary where they flow into. The microplastic separation method consisted of taking soil samples from the indicated points and sieving them with 850 µm, 1000 µm, 2000 µm and ?2000 µm meshes. The separation was then refined with the density method using sodium chloride (NaCl) solution. The MPs were sorted by color, shape, weight and size. Most of the MPs were observed to be irregular, square, rectangular, spherical, elongated, rigid, pink, white, blue, black, green, yellow, red and light blue. FTIR infrared spectroscopy was used to identify the type of polymer constituent of the MPS. In the Lurín river, polypropylene (PP), high density polystyrene (HDP) and polystyrene (PS) were identified; in the Chillón river, polypropylene (PP), high density polystyrene (HDP) and polyethylene terephthalate (PET) were found. The main sources of PM were anthropogenic activities, such as industries and waste dumped by the neighboring urban population. Therefore, the information found will allow managers to implement environmental improvement measures for microplastic pollution in watersheds.