The worldwide spread of microplastic and its potential hazard for the environment have been promoting scientific interests and public awareness. The increasing spreading of microplastic particles (MPPs) in the biosphere raises many questions on their (negative) effects on multicellular organisms. Currently, there is a common assumption that the entry of the nanostructures into vital biological systems could cause damage, which could subsequently cause harm to human health. However, the impact of MPPs (size ≤ 5μm) at the cellular level is mostly unknown. After enteral (i.e., through the gastro-intestinal) and/or pulmonary uptake, MPPs come in contact with the cells of organ lining tissues in particular the epithelial ones. From there, MPPs can be up taken by epithelial cells and / or penetrate more deeply into the tissues incidentally leading to a systemic distribution in the body. Macrophages, in their nature as scavenger cells, are very likely to get in contact with MPPs as well. Here, we studied potential effects of plain Polystyrene– MPP on cellular level. We used murine macrophages (ImKC, J774A.1) and epithelial (BNL CL.2; STC-1) cell lines. The particles size (0.2; 0.5; 1; 2; 3; 6 µm) as well as the particles concentration was varied systematically. Using confocal microscopy and scanning electron microscopy, we demonstrated a cell-dependent uptake of the MPPs. A putative cytotoxicity was analysed by standard MTT Assay. As further stress marker for cells, we quantified the intracellular quantity of reactive oxygen species after the MPPs uptake using a flow-cytometry-based detection assay.