The non-indigenous mysid Neomysis americana (S.I. Smith, 1873) is reported here, for the first time, along the Bay of Biscay in the Loire estuary, France in 2021. This species, originating from North-American estuaries, was initially discovered in Europe in 2010 (Wadden Sea) and first reported in France in 2017 (Seine estuary). The absence of long-term monitoring makes it impossible to know precisely the arrival of this non-indigenous species in the Loire estuary. However, this species is present in high abundance, suggesting an arrival prior to 2021. Its introduction might even be prior to or concomitant to the Seine estuary discovery, suggesting an introduction via the ballast water of the commercial vessels.