Over a 3-years PhD project we have investigated the acute toxicity of nanopolystyrene beads (50 nm) on oyster gametes (behavior, fertilization success) and embryos (developmental success), as well as subsequent repercussions of an early exposure at a sub-lethal dose on the larval and adult stages over two generations of oysters. In the acute toxicity experiments, dose-response effects were observed from 10, 1 and 0.1 µg.mL-1 on spermatozoa mobility, fertilization success and embryo-larval development success, respectively. Furthermore, the toxicity was dependent on the surface functionalization, amino-nanopolystyrene beads exhibiting the highest toxicity, compared to plain or carboxylic-nanopolystyrene beads, due to their high stability in seawater (aggregates ¡ 100 nm) and their positive charge increasing interactions with cell membranes. An early embryonic exposure at a sublethal dose reduced significantly the oyster larval growth (by 9 to 21%) leading to a delay in larval settlement but no long term consequences were observed on juvenile and adult stages in terms of growth, reproductive outputs or ecophysiological parameters (e.g. respiration and filtration rates). On the second generation of larvae, no significant effects were detected on the selected endpoints whether they had been exposed to early embryonic exposures at the first or at both generations, suggesting no stress-memory mechanism. An intermediate but non-significant growth response of oyster larvae exposed at both generations opens a question of further interest on the occurrence of adaptive response allowing higher tolerance. Overall, our results suggested a limited risk of nanopolystyrene beads for oyster early life stages according to the LOECs from acute toxicity experiments and data provided by our long-term experiment. Nevertheless, because the features and the current environmental concentrations of nanoplastics remained unknown, this assumption must be confronted in the future when methods will be available to quantify nanoplastics at sea providing accurate risk scenarios.