Microplastic contamination has been discovered in the most remote sections of the oceans [1] and in most ecosystems around the world. Sources of marine microplastic include rubber from tire wear, fibers from synthetic clothing, fishing nets, buoys and waste from the shipping industry, pellets of raw plastic material, packaging and bottles, overspill of sewage treatment plants and microplastic beads from cosmetic products. Exposure to sunlight, microorganisms and salt water degrades the plastic material over time, thereby fragmenting into ever smaller microplastic pieces. Systematic investigation of microplastic contamination in the ocean necessitates continuous monitoring to obtain high density data samples both spatially (to map the origin and effect of marine currents) and temporally (to understand long-term trends). Ideally, the data gathered should include detailed information such as particle counts, size fractions and composition. To date, most microplastic studies rely on samples collected manually at specific times and locations, which later are analysed in research labs using state-of-the-art techniques such as optical microscopy or Raman/FTIR spectroscopy. This approach provides valuable insights on the microplastic composition, but only a limited understanding of its spatial and temporal distribution, and it is labour-intensive and time-consuming. Within the framework of the EU Horizon 2020 project NAUTILOS, several compact and cost-effective sensors for autonomous continuous in-situ monitoring of ocean parameters are being developed. CSEM and NIVA (Norwegian institute for water research) are jointly developing a new in-line microplastic sensor, capable of analysing marine microplastic in an automated manner.