Plastic ingestion has been reported in wide range of terrestrial and marine organisms and it is considered a major threat due to its potential accumulation, which has been associated to false satiation effects or the release of potentially toxic compounds (e.g. plastic additives). However, data on the retention and potential accumulation/egestion of plastics after a prolonged exposure is scarce. In this study, we analysed the ingestion and retention time of nylon threads of varied lengths in the green shore crab Carcinus maenas as well as the potential effect of a prolonged exposure to nylon fibres through diet. Adult male individuals (n=16) were divided into groups and exposed to four different diets: control diet, diet with short fibres (0.5 mm), diet with long fibres (2-4 mm) and diet with a mix of short and long fibres (0.5, 2 and 4 mm). Crabs were fed 3 times a week (0.5 g of blendered mussels and 0.15% of added fibres) for a period of 21 days. Faecal pellet production was analysed throughout the study (weight was recorded and images were taken in order to analyse their dimensions) and the haemolymph protein content (Bradford assay) and body condition indices (condition factor and hepatosomatic and gonadosomatic index) were recorded and compared at the end of the study. Nylon fibres of all lengths were encapsulated and successfully egested through faecal pellets. Faecal pellet production did not seem disrupted by fibre ingestion, yet those with longer fibres were more easily fragmented. As other authors have already suggested, the gastric mill might play a key role on the accumulation of fibres, especially longer ones, as they took the longest to be egested and presented deformations (e.g. bended, molten-like defects) after egestion. No clear significant differences were observed on the total protein content or condition indices between diets.