For the very first time microplastics were systematically analysed in feaces of the endangered Mediterranean monk seal (Monachus monachus) in Greece, as a top marine predator. This study was carried out in a joint project by the Hellenic Centre for Marine Research (HCMR) and the Greek NGO Archipelagos – environment and development within the framework of the project “PLASTIC BUSTERS MPA”. Twelve samples were collected in monk seal caves along the southwestern coasts of Zakynthos island, Ionian Sea, Greece, according to a special protocol elaborated for this purpose. The set of samples was analysed at the HCMR. A total of 208 particles were detected 42 of which (19.2%) were identified as organic material and were discarded from the analysis. The length of anthropogenic particles ranged from 45μm to 28,763μm, though 75% of the particles ranged from 100 to 3000μm. Interestingly, 34.2% of the particles were smaller than 1,000μm and only 10.9% were larger than 5,000μm. Most of the particles identified were filaments (n=140, 84,3%), followed by fragments (n=24, 14.5%). Transparent particles were the most abundant ones (39.8%), followed by blue ones (39.2%). Red particles occurred in 7.8%, while green and black occurred in 6.0% and 3.0% respectively. Most of the transparent and blue particles were filaments (92.5% and 89.2% respectively). The majority of the particles identified were polyamides (73.8%), followed by polycarbonate (14.8%), and polypropylene (6.6%). Because all faeces samples analysed contained microplastics the exposure of monk seals to this pollutant might be a cause of concern. Further investigations are necessary for drawing firm conclusions.